I am torn between Tennant and Smith as my favourite Doctor. Purely on The Doctor it is Tennant for me because his broad acting ability saw him play eccentric and emotional scenes with consumate ease. Fantastic! as Eccleston's Doctor would say
The reason I am torn overall is that I preferred the storylines during Smiths era, it seemed to be more grown up and I love the childish and silly approach played brilliantly by Smith and yet the anger is there simmering away underneath.
Here are 2 of my fave scenes from Tennant and a longer video from some of Smith's best scenes (there are many more great one's):