Russell T Davies did an in depth interview with The Times on November 23, 2004 and was asked who was his favourite Doctor - he gave his answer by quoting what David had to say in another interview. Russell was filming Casanova at the time of the interview so I imagine he and David were talking about Who. David has stated in the past he spent a great deal of that shoot trying to get Russell to give him a part in the new series.
"Who was your favourite Doctor Who?"
"Tom Baker. David Tennant said in an interview that was really a case of a man and a part just meeting and the fireworks taking off."
ED NOTE: I think the same could be said of David's time as The Doctor as well!