Bit like asking who is your favorite James Bond, the first of course, Sean Connery, after that, its like having an actor play the part of the actor who IS James Bond,
To be fair to the Dr's, at least there is a story line that accommodates the change in the Drs physical appearance, non-the-less, my Favourite is still William Hartnell, he was an old Grandfather type fellow, that still had the cantankerousness one should expect of a man in his position.He had an other-worldly air about him.
My least favourite was Jon Pertwee, it was during his reign that I ceased watching Dr Who, with the silly props like his clowns car, he did to Dr Who what Roger Moore did to James Bond, turned something mysterious into something silly.
Now the very first film I saw, and at the pictures at that, was in 1965, Dr Who and the Daleks, nowadays, we are bombarded with amazing effects, but back the, you cannot imagine how incredible seeing this film was to us group of small kids from the Childrens home, it was like nothing we had ever imagined before.