GSP has a lot more diverse striking than Diaz. Diaz relies on his punches which are effective. GSP however moves around a lot, punches, kicks mixes things up with TD's.
sorry for the late response but does diversity matter if Diaz can dominate w/the same style over and over? plus we've never had to see him mix it up, we don't know what else he has in his arsenal, who could say w/confidence that GSP is a better boxer b/c i've never seen him dominate via boxing like Diaz has.