Toughest current guys to hold down on the mat

Whether it's their ability to keep their back off the ground after a TD has been successful, how they positioned themselves for the initial TD to be successful in getting back up (hips, legs, sprawls, whizzer, etc.), keep their back against the cage, wall-walking ability, sweeps, etc. Obviously don't include guys who have never or rarely been taken down or put in those positions like Weidman, Cormier, Jones, etc. Who are the toughest guys to hold down on the mat currently in MMA?

I'll list the first few that came to my mind: Edgar, Bisping, Machida, Rockhold, Condit, Gustafsson