As far as a MMA Artist IMO GSP is better than Anderson "NOTE" GSP to me is more rounded artist. Is he a better striker no, but his wrestling, Judo, TDD, and etc... is.
Anderson TDD didn't prove to good Sonnen 1, Lutter, and Hendo. Yes he won, but it showed his weakest link. To end Silva should win a match between the two just because of his strong area's not from being a complete MMA artist.