Nick Diaz will be the most well rounded fighter that GSP has fought since BJ Penn. All the guys you listed have obvious strengths which are their bread and butter, take that away and they aren't as good. Nick can scrap, brawl, or pick you apart, submit you, out work you, out heart you. He's a jack of all trades type of guy.
Still think GSP will win via dry hump, but Diaz has a better chance to win then Shields that's for sure.
"Let them see that their words can cut you, and you'll never be free of the mockery. If they want to give you a name, take it, make it your own. Then they can't hurt you with it anymore." - Tyrion Lannister