The shorter Nate Robinson will harrass opposing guards on defense, but can be shot over and posted up. Also, I have to agree with above posters, even though I have only seen a limited amount of Robinson playing. Rondo probably is the better point guard. Also, on offense and defense, Rajon's toughness, intelligent use of his A+ quickness and body control make him play bigger than his 6'-1" highth. To Nate's credit, its possible he is the better shooter.
When you compare both players total overall "games", Rajon Rondo is a grade A player, Nate Robinson is a grade B player.