if it were just the two of you and maybe the 12 year old...I'd definitely say Luau. The Backyard BBQ, IMHO, is really for people with younger kids. The characters are there and they dance and interact quite a bit with the quests. My DH and I went this summer and it really wasn't that great for us - kind of boring. The food wasn't so great either.
The luau is a fantastic show - absolutely wonderful. Again, we didn't like the food but it was worth it to see the show.
PamNC