My 2p...
David Tennant: Brilliant. Got the role down to a T, and delivers the one-liners splendidly - right from his first episode, where he tosses in a reference to that other great archetypal Englishman in Space, Arthur Dent.
Catherine Tate: not as tasty eye candy as Agyema Freeman, but was extremely funny in the 2006 Christmas Special (Remember the "Pockets!!" line?). So I'm prepared to with-hold judgement until tonight's episode.
Having said that, my favouritest line ever was when Rose Tyler asked Christopher Eccleston:
"If you're from another planet, how come you sound like you're from the North?"
"Lots of planets have a North."