This has to be one of the hardest questions EVER. I mean, for me, the entire cast all just works so well. But thinking of this as a forced-choice question...
Among the Doctors, I loved the Tenth. Frankly, I could not bring myself to watch Series 5 for the longest time because I knew I'd have to watch someone else play MY Doctor.
(On an off-topic point, did you guys have that feeling too, when having to watch the transition between Doctors? I mean, my brother, who had gone ahead and watched Series 5 said I was being overly sappy but...but...but...)
I did like the Ninth a lot (he was my first Doctor), but after seeing the Tenth, I started to see that the Ninth was so much darker.
The Eleventh--oooh, I'd say it's hard to place him beside the other two. Dunno quite why. It's not that he's less anything. I mean, I do enjoy him a lot. But I think his mix of wacky and serious is far more polarized that sometimes, he comes across as scary--though that is part of his charm too. So I dunno. razz
Among the companions: by herself, I liked Rose Tyler best. She was a stand-alone character, and she was tough. She wasn't some emotional ice queen either--just nice and well-rounded. While I did love the chemistry between Donna and the Doctor, I sometimes felt that Donna was somewhat defined by the Doctor. I mean, in that one year they were apart, she was just waiting. Not that that makes her lousy or anything, but I loved Rose's drive.
So there. Whoa boy, sorry for the wall of text. I got carried away. 3nodding