I've only seen the last four Doctors, so unfortunately my list is pretty short:
1. Eleven - He's been around long enough now that I can comfortably put him above Ten in my rankings. I was hooked from the very beginning but wanted to make sure I wasn't just saying he's my favorite because he's the current Doctor. Now, though, I think I can safely say that he really is. I love where Smith is taking him and I can't wait to see how he continues to evolve with his new companion.
2. Ten - My favorite until Eleven came along. I think he was at his best in his middle seasons, with Martha and Donna. I'm not a fan of his "romance" with Rose (who's also one of my least favorite companions) and that brings him down a bit for me, and I was really starting to get tired of his antics by the end of his overindulgent "farewell tour."
3. Nine - I just don't think he was around long enough. I did like what I saw from him, but I wish I could have seen more. I also didn't think he was alien enough, he was a little too human to me both in looks and attitude. I loved his fire, though.
4. Eight - Again, like Nine, there just wasn't enough there, but I still liked what I did see. Not a big fan of the half-human thing, though, and I'm glad the new series seems to have brushed that under the rug.