I like them both equally. David Tenant set the bar really high, and for me, at least, Matt Smith held up that standard. I think that David's stories and episodes were more interesting, but that's only the writing; acting- wise, I don't think Matt is worse than him at all. After Season 4 ended I never thought the 11th Doctor could ever match up to David, but surprisingly, Matt Smith did.
I wish Season 5 and 6 were as interesting as the ones before, though. 'Blink', the Agatha Christie episode, and 'Silence in the Library', and all the specials and season finales with David Tenant are still the best episodes on my list. On the other hand I found 'The Girl Who Waited' a bit boring, and a lot of the newer episodes don't have that thrilling storyline.
I just hope the next one is as good as them, because after these two it'll be really hard to get used to one who can't uphold that brilliant, entertaining Doctor personality as well.