Tennant's best episode was Midnight, I think, because he really couldn't overact and that made it so much better. Or possibly Waters of Mars.
So many of my issues with Tennant's era are more down to RTD than Tennant. It took me a while to realise that it wasn't that I disliked Tennant, it was that I disliked Davies. But while Davies wanted to make the Doctor into Jesus, Moffat is so busy messing with our heads he seems to have forgotten how to write good Who. Hopefully that hasn't leaked over into Sherlock.