David Tennant! Everytime I watch an episode with the 10th doctor I walk away happy, even in the most depressing episodes!! I can't put my finger on what Tennant brings to the table that I love so much, but I would almost say the 10th doctor is my all-time favorite character, regardless of the show. I'm sure the writing has a good deal to do with this as well. I think it's a prime example of harmony between actor and writer.