Doesn't get much better than Shields, at least in terms of MMA grappling. Roan Carneiro has some very good BJJ credentials but he's been subbed multiple times in MMA.
hard to think of Shields as a submission guy, he's more of a lay n' pray guy.
I'd say Nogueira, Fedor, Jim Miller.
Carlos Newton by Saku. Maybe the best grappling match ever in MMA
Mir subbed Traven.