I have been to both and definately liked the Hoop de Doo better, even though the Luau show something that would normally be much more my style. We had a lot of trouble seeing at the Luau (they arrange long tables that seat 6-10 perpendicular to the stage and our party was seated at the back half of one of those tables-- so we were craning over other people's heads the whole time). The food was merely OK and the show nice, with a series of performers demonstrating various dances from different islands of the pacific. Some of the dancers were women with hula and similar dances and some men with fire (and other) manly dances. I remember feeling like this show was overpriced, and I would be ok with going back if I were traveling with someone who really wanted to see it. But I wouldn't go under my own volition.
The Hoop De Doo was a different story. I got dragged there by my cousin who assured me the dinner and show was great. I am by no means a hoe-down type of girl, but I had to agree this show was very, very amusing. Lots of corny jokes and embarrassing audience participation. Food is basic american fare, but of good quality and unreasonablly large quantity. The ambience is a western saloon and it is well done. I did not expect to like this show, but very much did. So much so that I went back with this same cousin (she lives in Orlando) at another visit. I actually enjoyed this Hoop Dee Doo much less, because we had front and center seats and I was in mortal fear of being dragged into some audience participation embarrassment (its funny when its other people, but would be dreadful if it were me up there...). Having seen this show twice, I am pretty satisfied, but every time we go back to Disney, I toy with the idea of seeing the Hoop Dee Doo again. I consider this show to be an excellent value.
I would offer one disclaimer in that the Luau that I went to was about 3-4 years ago-- and it is my understanding that the show has changed since then. I am not sure how much. So some of what I have said may no longer hold.
A second thought I just had was that I did see this show when I was a kid of maybe 12 years and I remember thinking it was very cool and exotic at the time (I was influenced by the Brady Bunch in Hawaii episodes, perhaps). So you might factor in the kid factor if traveling with older children or young teens.
Hope this helps.
Beatnik