The castle, no doubt. Last time I took a 4 year old to the luau show he fell asleep during dinner and didn't see any of the show anyway. The kids were all bored to tears.
We did the 8:00 show and our DD4 enjoyed it. She really liked the beginning part of the show. But laid in my lap during the main part after we ate. She did perk back up quite a bit during the fire part though. She still talks about that. She enjoyed the Hoop Dee Do more though.