Chuck Liddell without a doubt. He has been a big name for so long. He had a tremendous run in his prime and even afterwards, he just happened to fall off the wagon towards the end.
GSP is a lock. He is probably the greatest welterweight to step into the octogon, him and Matt Hughes. Speaking of Hughes, him too, he might be a dick, but look at his game, it was flawless. What a dominant fighter just like GSP, of course GSP is way better. GSP is well rounded in every element of the game and just keeps squashing everyone in his way.
Anderson Silva. Must I say more? I think not.