Without doing any quick research, I'd say Jacare. [ame]http://www.youtube.com/watch?v=9aAbd3HM960[/ame]
Yea Roger is nasty. Marcelo also has some of the most beautiful BJJ you'll ever see. I think skill wise he's at least on the level of Jacare.
Well, if you're talking all-inclusive grappling, you have to not only include BJJ, but also wrestling. That is a form of grappling as well. Albeit a kind of narrow one in terms of utility relative to BJJ. Now when you're talking about Gi Grappling, No-Gi Grappling and grappling in MMA...you're talking about three VERY different things. So, who has the most experience at the highest levels of all three? There really is only one stand-out in my mind which is Demian Maia. World Champion and ADCC Champion (No-Gi) and has fought at the highest level in MMA and utilizing his BJJ in very different and in many ways, more difficult circumstances then would otherwise be found in a pure BJJ environment. Tough call, but based on the context of the question, I'd have to say Maia. Not just because he's done it at the highest levels of all three types but he's also found great success as well.
Probably the best of the ADCC because technically they are all round grapplers but in MMA then your grappling has to lace in well with other martial arts. I'd say GSP in MMA grappling and Roger or Jacare in pure grappling.
gsp is very very good with his wrestling and bjj mixing together very well but if you cant sub hardy (a purple belt) your not the best mma grappler! imagine if some1 like maia had hardy in those positions every minute of every round he would of been finished!