Each Doctor is good in their own way. I liked the Ninth Doctor from last season, and it would have been interesting to see another season with Christopher Eccleston.
I've got to say that the Tenth Doctor is one of my all-time favorites. His relationship with Rose Tyler gets a little too close for my liking. I'm not used to seeing the Doctor in a romantic situation. He's an alien, and doesn't usually get too close to his companions in that way. They don't become physical, but the tension is definitely there.
If you're not familiar with the classic series, the actor playing the Doctor changes every few years. They've done it nine times since 1963.