What are the pros and cons of each and what is best overall? I've seen all these different variations in existence and have a rather small understanding of it.

There are two main groups of metal halide : quartz (older) and ceramic (newer). The quartz is basically a mercury vapour lamp with added salts to correct colour rendition. They typically only get to about 60ish CRI, which is better than most "colour corrected" mercury vapour (/DX, /N, etc). Then came the ceramic metal halide, which is basically a modified HPS arc tube (same ceramic material) but shaped more like the quartz metal halide ones. It also, I believe, has more mercury than a HPS lamp. They are of course all pulse start. With careful dosing of salts, combined with fine tuning the pressure (which takes it a step further with electronic ballasts), the CRI can be improved to over 90.

PowerBall is merely Osram's  (and by extension, Sylvania's) trade mark name for their line of ceramic metal halide. Philips has CDM, PowerTone, while GE has ConstantColour.

I find myself preferring the Osram/Sylvania PowerBall lamps because, to my eyes, they are more pleasing. Of all ceramic metal halide, the 3000K PowerBall lamps resemble incandescent lamps the closest.

We've got a 150W Powerball lamp, I agree that the 3000K is excellent and the one I prefer if needing white light.

I'd always thought the Powerball lamps also had a more spherical arc tube compared to the older Philips CDM line. Of course, the newer Philips CDM lamps all seemed to have adopted the spherical arc tube too as opposed to the cylindrical one they originally had.