It seems that the widely accepted "best" socket in the work is the UK BS-1363 (type G) socket. This is a pretty decent opinion, but I personally think it is the second best socket in the world. Here is why:
 - Ground prong is the same width as the live/neutral pins, just longer and unshrouded. This means that with a cruddy noncompliant socket that doesn't have a wide enough flange (common with international sockets), you can insert the ground prong into the live part of the socket, energizing the chassis of the appliance.
 - They are sharp, of course I haven't ever experienced this myself because I live in the US but apparently the rectangular beveled pins of the plug are very very painful to step on, especially since practically all of the plugs are of the right-angle style that can stick up when laying on the ground.
 - If you have a screwdriver then you can shove a Europlug in it, potentially damaging socket contacts

The plug that I think is the best (with conditions) is the type M plug (BS-546), most notably used in the UK before the late 1940s when they switched to type G, and currently used in countries like India and South Africa among others. Now the type M plug I believe is still made in unshrouded pin and unfused versions, and I believe the sockets are also made in unshuttered versions. But shrouded, fused, and shuttered versions exist, which maintain equal safety to type G with the following benefits:
 - Ground prong is too wide to fit in live/neutral parts of the socket
 - Rounded ends probably greatly reduce the pain associated with stepping on them
 - Completely incompatible with most cruddy international multi-fit sockets (a good thing, really)
 - Can handle up to 15A instead of just 13 (not as important for existing applications of course)
 - You can't shove other country's improper plugs inside them with just a screwdriver

Now obviously the UK switched away from this plug for a reason, because their ring mains could deliver up to 32A, and that required every plug to have a fuse. This could have been done with type M, but older plugs and sockets would still exist that remained unfused, unshrouded, and unshuttered. They made the right move in my mind. And all of the drawbacks of the current type G are really just nitpicking. But my viewpoint stands, type M is probably the best, assuming the sockets are shuttered and the plugs are fused and shrouded.

Also on a side note: Australian (type I) outlets are based on blades, like US plugs. New type I plugs have shrouded pins, proving that it is possible to make shrouded pins on a blade-style plug. Why doesn't the US do this? 120V can still really hurt you.

What do you think?

Aussie sockets have switches, so there isn't arcing! I never understood why the USA didn't do that.

@Baked bagel 11
Almost all of our appliances have switches on the actual appliance, that we would typically turn off before unplugging. I think Technology Connections made a video arguing both sides of the topic of switched outlets, I don't really know where I stand on that issue. In my mind, switches gotta be somewhere, doesn't matter where you put them. Switched outlets do exist in the US and are cool, but not often. Oh well.

Well, "simple appliances" (that is how the standard here used to call such devices; like hot melt glue guns, cloth irons,...) don't need switches, they can be controlled just by unplugging them. If done too frequently in one socket, you wear it down at it loses connection sooner or later regardless what mains socket standard we are talking about. Having a switched socket prevents that from happening, but on the other hand the switch itself presents more wear prone parts of the installation.

And for the British mains socket/plugs: Weren't they originally designed to work in 25A or even 32A circuits? So their design needed to anticipate at least 32A upstream fusing. Therefore the need for such beefy construction and the secondary fuse within the plug, as the 32A fuse won't be able to protect the cable from the plug to the device (or the cable would have to be too thick to be practical).

Most (practically all not based on the British one) other standards limit the maximum fuse (breaker) rating for domestic circuits to just 10..16A, so the branch fusing becomes sufficient for practical cable sizes without any need for any in-plug fuse. And allows the sockets/plugs to be way more compact.

So when judging safety, I won't agree the with the statement of the British system to be "the safest", when relying no moron would replace the blown fuse in the plug for a nail or so. With standards from everywhere else the cable is just protected by the breaker in the panel.
Yes, at the time of its origin, the power limitation the other systems impose semed as impractical, at that time the need was to quickly reduce the use of local coal burning stoves and convince people to use electric heaters instead, therefore the need for the rather high power sockets in homes.
Other parts of the world did notface that problem, so did not need such high power capable mains socket system, so went for simpler and more compact solutions.

But if you look on any modern wiring, there use to be way more branches than would be needed if the power rating would be the limit. So no need for 25 or 32A capable socket anymore, then the British standard (of such oversized sockets/plugs) becomes more of a historical relic than anything useful. But as with any other such standard, once set, extremely hard to change, even when others may be way better suited for present day needs.

I think our Swiss type J is the best. Bescause it’s small, safe and in some cases the 230V plug (T12 or T23) can be plugged into a 230/400V socket (T15 AND T25)

https://en.wikipedia.org/wiki/SN_441011

@Medved
While yes these sockets were installed on 32A circuits, each socket itself was only rated to carry 13A maximum (the largest fuse that could be safely installed in a plug).

And yes I am making a lot of assumptions here. Assuming the plug has a fuse, assuming the pins are shrouded, assuming the socket is shuttered, etc. Assuming all of those conditions are true, this system is safe. But there is no way to ensure that, which is admittedly a problem.

@Michael
Type J seems relatively similar to others like H, K, N, and O. Often no safety shutters or fuses in the plugs. Which is usually not as much of a problem since the maximum circuit size is 23A (but more often just 16A), but the conductors in the cords seem to not reflect that, just like the US. At least they have shrouded pins, that is definitely a good thing.

Interesting note on three phase compatibility, I did not know that. I can see how that can be useful.

BS1363 has its own safety/performance issues

1
Wiping a flat blade with a flat (in one dimension) socket contact results in moderate pressure, for the same amount of force the user inserting the plug feels from outside

In European plugs with round pins, the pressure from the socket contact is concentrated to a narrower spot, resulting in higher pressure, so the contact is wiped more forcibly in this spot to break surface dirt and oxides

The same contact spot is then elongated into a line when the plug is fully inserted. The final contact area is similar to the BS1363, except in the European ones the line is along the pin (along the same area that is wiped on its way in and out), while in BS1363 all the area that was wiped during the insertion of the plug isn't even in use and the benefit is wasted



2
The plug is polarized, which gives the appliance manufactuer (or DIYer) a sense of security that a certain conductor at their end has no voltage on it. This sense is false. It takes as little as pulling the plug halfway out and a little to the right to make the appliance live on the Neutral as much as it is on the Live

Anyone referring to this as a safety feature (outside of some industrial applications maybe, which would then use IEC 60309 plugs anyway), does this because in their thinking, they treat the Neutral with less caution than the Live. Which means their entire application is less safe regardless of the plug

Schuko and the Italian types are not polarized, and while the French plug itself cannot be inserted in reverse, there is no consistent code for the polarity of the wiring in the wall receptacle. (Besides, the plug itself is usually the same plug made to fit both the French and Schuko). This means that all 3 are essentially non polarized

Then manufacturers and DIYers using European plugs can have no expectations regarding the Neutral, cannot treat the Neutral in any way less carefully than the Live, and insulate everything properly

This have nothing to do with the switch of the appliance having 50% chance of being on the neutral. When this happens, when switched off, the appliance internal wiring and components will remain live, but they are still fully insulated and enclosed



3
If an appliance connected to the plug has a short circuit in it, there will be sparks and the breaker will trip or fuse will blow

MCBs (European type circuit breakers, used both in Europe and UK) are all energy limiting. When a short circuit with high enough current happens, they interrupt the current before it reached its Ohms-law expected peak value, and respectively the energy. This effect is most significant when the short circuit current is high, ie. house near
the transformer, socket on a short wiring run from the DB inside the house

This reduces the arc and melted metal blown from the contacts that were closed to complete the short circuit (the plug, held in hand at the moment this happens)

For exact specs see https://www.eaton.com/content/dam/eaton/products/electrical-circuit-protection/circuit-breakers/xeffect/eaton-xeffect-industrial-switchgear-range-catalog-ca003002en-en-us.pdf plots on p. 152-153

I have not been able to find similar data for BS1362 fuse

The BS1363 plug is inserted into a receptacle on a 32A breaker, the European on a 16A breaker. At high currents, the 16A breaker will significantly reduce the "bang" compared to 32A

Back in the day when BS1363 was designed, short circuit currents in homes were small (probably in the <1kA range), and the only means of upstream protection was fuses - but in the UK they were often not sand filled - just user replaceable wire between 2 screws on a ceramic cartridge, so the BS1362 fuse performed better than the upstream protection



4
Any short circuit interruption device (breaker or fuse) has limited interruption capacity, and will blow up if this capacity is exceeded. For BS1362 fuse it is 6kA, same as circuit breakers mostly used in homes

Maybe holding the interruption device (plug with the fuse in it) in hand while it is failing (for example, if the ceramic was cracked during installation into the plug), is less safe than having it installed remotely in the DB



5
Additional connections in the plug mean additional possible points of failure (bad contact and heating), which cannot be seen by the user from outside, and cannot be felt by the user from outside (the plug won't feel loose in the socket when inserting). The plug with loose fuse may be plugged in behind some cupboard, in a hidden location where it can keep heating and melting until it causes a fire

Any other plug is safer here just because it is simple, there is lower chance that something is bad inside

Same for the switch in the sockets (Australia too). Besides, i wonder how well that switch is protected from molten copper shooting out around the button edge if it is switched on into a short circuit



Does this amount to make the plug bad/dangerous enough to avoid it ? No, it is a fairly safe plug, as are most others used around the world, many of which do or dont have some safety features in particular

Just cut the hype already



If i would be choosing one plug of the existing ones for "home" uses in e.g. a new country (without compatibility considerations to existing everything), it would be Schuko (best) or the Italian (more compact, allowing to fit 2x more sockets in the same space)

In Italy they actually do use both for those very reasons

There are other European plugs with similar quality - the French etc, but they dont have the feature of being possible to insert both ways (for convenience and for reducing strain on the cable in some cases) which is a nice to have

Swiss 3 phase and 1 phase combined sockets are also nice to have. With minor changes the swiss combined socket can be made to accept also the italian plugs, and the Italian and schuko sockets can be made to accept the 1ph Swiss plugs

@Ash
Very interesting view on polarization, I haven't heard it described in that way. I always assumed that insulation requirements for neutral were equal to the requirements for live, but I could be wrong.

I had no idea that MCBs were energy limiting!!! I wish we had those in the US. I can see how that would definitely make a difference in terms of the "bang" of faults.

6kA is not a whole lot... Lowest I have seen here is 10kA.

My viewpoint on type F Schuko is kind of mixed. They can fit perfectly into type H, K, L, O, older round type C, and sometimes type D sockets, but won't receive a ground connection by doing so. The same applies for the type E French plugs.

As to Italian type L plugs, I am so far a fan. 16A, unpolarized, protruding ground pin, shuttered sockets, shrouded pins, seems good. Reminds me of a stage pin connector, but not stuck in the 1930s lol. Europlug compatible, which is nice. The problem still stands with it's compatibility with type E and F that won't get a ground connection, but yeah I can see how this is a good choice.

E plug can not fit into F (the grounding pin is in the way) and vice versa, F-only plug can not fit into E socket (the ridges on the edge and the grounding contacts are in the way of the round plug shape).
Only the combined E+F plug (virtually the only one produced for class I devices for continental Europe market since way before 90's) can fit into both, but then it receives the PE connection in both E and F sockets properly.

For the assumption of polarity: Yes the standard may state that the N needs to be isolated the same way as Live, but people are often forgetting that and tend to wrongly assume the N as "safe to touch".
With nonpolarized plugs/sockets it is clear from the start there is no guarantee which one would be live, so people are really careful and treat both properly.
Of course assume people who know at least some basics what the electricity is. If someone has really no idea at all, then nothing can save them if they start to poke inside...