S'mon said:
Interesting that no one has voted 15th-20th yet. My experience of 1st ed AD&D at those levels was that the PCs tended to dominate their surroundings and there were few good challenges - after all 'Queen of the Demonweb Pits' was for 10th-12th level! - but 3e is specifically intended to be playable at all levels.
I think I'd like to play 15th-20th, but I've never actually done that (or anything beyond it). So I voted 9-14, where I've had a lot of fun with various characters.