I've played nearly every edition of D&D (at least a session or two). I've played Basic, 1E, 2E (the first edition I played), 3E/3.5, 4E, Pathfinder, and a few retro clones. While I enjoy all of them I have to say that 3E/3.5 is my favorite edition. Pathfinder is so close that I think you could lump it in with the 3rd era (as some companies call it). Again, I like all of the systems for various reason, but 3rd era made it easy to make whatever you wanted. Unfortunately it also let you make whatever you want (which lead to some ridiculous builds and character concepts). I also loved the OGL. Yes it flooded the market and you only need so many fighter books, but still it lead to some great 3rd party content.
All this said, I'm really looking forward to 5th edition.