Been to all of them, and the two that I didn't vote for are HDDR and The Wave. HDDR was a very funny show, but it's not the most interesting food (although it was very tasty, and I think doing it at least once is worth it). The Wave disappointed us last time - I received a bad piece of fish and couldn't really eat it.
Now for the other four:
-Ohana is a fun place to dine, and the food is very tasty. I enjoyed all of the meats, which have a nice oak-grilled flavor.
-Brown Derby is my favorite restaurant in DHS. The cobb salad is delicious and filling enough to be an entree.
-California Grill is my second favorite signature (behind Artist Point). Aside from the pretty view of MK and the lagoon, I've had some great dishes here, including sushi.
-My last meal at Yachtsman had some highs and lows, but the bread, appetizers and my dessert were all amazing. I chose my entree badly, but I definitely want to go back because most of the food was so good.
In terms of priority, I would definitely say California Grill, Ohana, and Yachtsman are highly recommended. For the fourth, HDDR or Brown Derby. Even The Wave is a pretty good option, although I'm not in a rush to return. Overall you have some good places to choose from.