In which D&D edition were player characters (PCs) individually most powerful?

[icefractal]

Needs more elaboration. I'm pretty sure either 3.0 or 3.5 is the answer, but it matters:
* At what level?
* Average character, optimized but playable, or maximum theoretical power?

If we're talking about an "average character", then the answer is all over the place. I'd say 4E probably has the highest "floor" - most characters are going to be fairly competent. On the other hand, some classes from 3E are going to be more powerful even right out of the box. And this is where pre-3E has a chance - a lot of spells were individually stronger there, and a Magic User with the right stuff could probably trounce a non-optimized 3E one.

Optimized but playable, I'm going to say 3.0 (because Haste and things like it), up to the point where Shapechange becomes available, then 3.5 after that. Although even then I'd say the 3.5 char is likely to have less weak points.

Maximum theoretical power is 3.5, not even a little question. Wish is capable of more, Astral Seed and Ice Assassin exist, enough said.