Hard choice, even though i appreciate good drumming, it's probably the instrument (apart from bass-guitar) that i focus on the least in the music, and it has to be really unique and cool-parts in order to make me go "WOW".
Mark Heron (Oceansize) is one of my personal favorites, i especially love the special vibe he gives to certain songs, songs like "An Old Friend of the Christie's", "Commemorative 9/11 T-Shirt" and "Massive Bereavement" where the drumming adds loads of atmosphere to the song.
Gavin Harrison (Porcupine Tree) is another example of a drummer i like, though when it comes to PT, the drums aren't the thing i focus on the most.
It's kinda hard to explain, but i feel that... SW's songwriting-skills (aka. making catchy and great songs) kinda stands in the way a bit, with a lot of other bands i love i can appreciate all the aspects, but when it comes to PT i rarely see it like that.
Obviously being a DT-forum i should mention Mike Pornoy, but he has never really been a personal-favorite.
He's good though.