I once knew someone who gauged Danny Carey's prowess as a drummer by how difficult it was to play Tool songs on rockband.

I cannot choose between Danny Carey and Nate Smith as a favourite drummer. Extremely different styles, but both hurt my brain. Danny's use of polyrhythms and constant shifting of time signatures, coupled with extreme technical difficulty. Nate Smith pushing and pulling time, crossing the bar line, and defying time.

I just remembered Joe Morello so maybe they're battling for second place.