Just doing the 3, since I haven't seen the ones that came before 2005.
Chris Eccleston - Yeah he only had one season, but I really liked the range, from comedic to dark and everywhere in between, and I really do wish he would have stayed on for a season 2.
David Tennant - Basically because he is just not as quirky as Smith's Doctor, at least in Season 6
Matt Smith - He could take the two spot after this season though. He's showing a more serious side and that's what I've wanted for a long while. His role in The Snowmen was really good and really eye opening.