I've often thought that it is hard to compare all the drummers, because they haven't all had the same opportunity to play the same kind of material, and some played mostly or only live (Terry Williams, Chris Whitten), and some played mostly or only in the studio (Omar Hakim, Jeff Porcaro).
Personally I like Pick best, but I think Omar and Jeff are probably the best drummers MK has played with. I think Danny did a great job, and wish he would have gotten more of a chance to show his chops on the two albums he played on.
A year from now we'll all have a clear opinion of Ian, I'm sure!