For my money, in competition and recent competition Saulo & Xande Ribeiro are up there.
Its hard to deny Roger Gracie's domination...and to win nearly EVERYTHING by sub, everytime.
Pablo Popovich is also super tough, a genetic freak, and he recently defeated Marcello.
Marcello is just the most fluid of them all in my opinion, is a small guy, and makes it all look easy.
Leo Viera should always be mentioned.
Although they're not beating any of the above mentioned folks anytime soon, I love Jeff Glover & Bill Cooper's style and they're the most entertaining to watch to me.
And finally, superheavy-wise...i don't see anyone giving Barnett too much trouble. He really is one of the best grapplers out there, and if you've ever rolled with him, it a rather miserable experience. He's DEF that guy you dread rolling with cause one way or another, its gonna hurt.