NOTE: THIS IS YOUR OWN EXPERIENCE WITH EACH TUBE AND IS YOUR OPINION   
OK lets start with T17 and down

T17: From what I've seen they leave a faint blue image in my eyes but not enough for me to notice

T12: Same as T17 but I can't be close to it

T8: Depending on the wattage it could put a sharp blue image in my eyes and hate it if it's placed under my eye level (5'9")
 
T5: IMO the worst for your eyes, puts a blue image so sharp in my eyes that it stays in there for more than 180 mins

Summary: Well from what I said it's clear that T17/T12 is the least harsh for my eyes

If we compare lamps of the same type, the luminance will be inversely related to the tube diameter

It is generally assumed, that luminance more or less equals glare/harshness, but this is not correct. Factors like the contrast between the lamp, its immediate surroundings (in the wing reflector, luminaire ballast cover) and less immediate surroundings (ceiling) play a role too

But do you compare fairly ? (or do you want an answer that is influenced by those factors as well ?)

 - Lamps have different Phosphor types so different efficiency (brighter lamp in the same size ...) and different spectrum

 - Lamps have different power densities. Disregarding some extra losses at the cathodes, F20T12 and F40T12 are 10W/ft, F8T5 is 8W/ft (and actually much less, since cathode losses are very noticable in such small lamp), and a 8ft VHO lamp is 27W/ft

 - Some lamps are underpowered, such as anything T12 in the US

I find that T8 is best for vision, because of no noticeable 60Hz flicker. And I like 4100K the best, because it seems the most balanced in color, and is great for general use..

The flicker is double the line frequency, 120Hz for 60Hz line or 100Hz for 50Hz line - except at the electrode of the lamp or when a lamp is rectifying. This have never been a problem for me

Triphosphors lamps tend to have longer afterglow, that further smooths out the flicker