Ecclestone was different and interesting, but I don't think he hung around long enough to be able to be my "favourite". Tennant was...well...I liked him at first, but then the scripts kind of started turning him into a Messiah-Sue who was known to everybody, which kind of defeated the point of Doctor Who. It was very modern, and very "Russell Davies", but kind of grating eventually.
Smith is my choice, because he's a lot more like the older Doctors - a daft old man, but in a young man's body. He conveys more of the impression of being hundreds of years old.
If you were to have asked me about the old ones though, Pertwee all the way. Sea Devils, Cybermen, Autons - he had to cope with the lot of them!