It's easier for me to point out my least favourites than my favourites because almost all of them I greatly enjoy.
I don't like Six at all, however much I try to get into him, and Seven is too goofy (and Sylvester McCoy is just not a great actor IMO).
Eight I discount completely to be honest, because he's only in one story (and no, I don't listen to audios) and it's an awful one.
One, Two, Three, Four and Five are all equally excellent for me and I love how wildly different but always believable their takes on the character are.
Nine, Ten and Eleven are my Doctors, because I'm not old enough to remember the classic series. If I was pushed I'd say Ten, but there is more than a little of personal feelings/nostalgia in there, because the peak of my Who obsession coincided with his Doctor. Plus it is just an amazing era of the show, and David is pretty damn brilliant.

Matt is incredibly promising and I rate him pretty highly but it's too soon to make my mind up and I always find it difficult to judge the current Doctor alongside the others.