Polynesian Cultural Center: Don't forget that since it's run by the LDS church, you can't get alcoholic beverages, and the pops are all caffeine free.
When I was on Oahu, I went to the Paradise Cove. It was okay, and I'm glad I had the experience. If you're going to Hawaii, you should definately hit a luau even though it has become a tourist trap. The one thing that disappointed me was that they didn't serve the po (I believe that's what it's called; the liquid bread stuff made from taro root). It said in the brochures that they served the stuff, but they didn't have any when I got there. I guess they didn't serve it b/c most people didn't like it and they were probably wasting a ton of it every night.
If you're going to Paradise Cove, I'd recommend the buffet rather than the served dinner if you like to eat a lot. I think I would have preferred the buffet b/c I got sick of asking for more food, and they weren't that speedy with the service. Also, the ulimited drink package is a waste. You don't have that much time to get drunk, and the lines are long so you never get your money's worth.