I, personally, dislike the woman at 'Ohana. I'd agree with the term "cheesy".
The luau is more of a stage show, with a little interaction with the kids at the end. Some of the entertainers are quite talented. If you like High School Musical, you'd probably like the luau. I thought seeing it once in a lifetime was enough.
The difference between 'Ohana and the luau enjoyability, IMO, comes down to the ability to ignore the performances and concentrate on the food. At the luau, food is brought out and the show interrupts dinner occasionally. At 'Ohana, you can ignore the show and just eat. The luau set menu is merely ok. Imagine the difficulty of serving 200 people at once, and you can imagine why some stuff came out less than piping hot. 'Ohana isn't trying to simultaneously serve the same courses, so everything is served hot. At the luau, I don't think I saw a single person ask for a second serving of anything. At 'Ohana, they'll ask you if you'd like more of a dish that obviously was enjoyed by the table (more bread pudding and pot stickers, please!).