I've been to a couple luaus on Kauai, Maui and the Big Island. The best one i'd been to on Maui was the Old Lahaina Luau. Though the Feast at Lele is delicious! Actually, I may be leaning towards the Feast at Lele. They offer course after course of perfect dishes, and you get your own private table.
On Kauai, go to the the Grand Hyatt Kauai Luau. Big Island, go to Waikoloa Beach Luau. I haven't been to any other luaus on the Big Island, but this one was a step above most. I usually book my seats through www.mauihawaiiluau.com. Try looking around for better prices, but I think this is the best one.
After all being said, I think The Feast at Lele was best. Waikoloa is runner up.