As someone who's been playing since I got my blue box set in 1979, I think I've given all editions of D&D a fair shake, including 3e, 3.5e and 4e.
However, I'll be up front here, and say that I prefer 3.5e over 4e, just to get that out of the way right off. I'm not a 4e hater, it's just not my...