Both are good, but I like Tusker House better. First of all, though the character interaction is good at both restaurants, I prefer Donald and Daisy to Lilo and Stitch.
The service is always great at Tusker House, the server I had at Ohana was average, but she did something that always irks me, otherwise I wouldn't remember it at all. But all the servers at Tusker House all seem to have a great sense of humor.
The food is good at both places, but the food at Ohana is very normal American fare, which I can get at home. Except for the breads, which are fabulous. The buffet at Tusker House has quite a few unique items, and I don't think I've ever had anything there I would consider bad, plus I love the bread pudding and the sweet potatoes.