I'm speaking technically.
What would you say? I think it's a close call especially between CC and TB. Slipknot on the other hand also has a few pretty technical songs.
Obviously not Slipknot. Cannibal Corpse are pretty bland death metal, two or three albums that are pretty good. I've only heard a few songs from The Berzerker but they were pretty damn annoying. Carcass win pretty much by default.
I'd say Carcass as technicality includes tonal/structural technicality as well as just playing hard stuff really fast. Carcass' range of styles could also be considered technical ability, to some extent.
But how do you know that Slipknot could not play stuff like CC if they wanted to? Slipknot is obviously making more money than CC maybe that's what they want.