I would probably opt for the later ADR, because most reports indicate that R&C does not accept table requests. You are welcome to make the request, but be prepared to be told you have to take the next available table (regardless of location) or you forfeit your ADR.
In general R&C is a pretty fast meal. It takes my family about an hour to have a three course meal there (whereas most other TS locations takes 75-90 minutes). As the PP said, wait times can be inconsistent. I've waited almost an hour to be seated (with an ADR) and I've been seated within 5 minutes. There hasn't been any consistency when I've gone. Assuming they're not running really behind schedule, I think the 7:50 pm ADR would be better timed in terms of the meal. You'll probably be between entree and dessert when it's time to go out to watch the show from the viewing area (if you don't get a patio table). On the other hand, I do think there is very little chance of getting a prime patio table at that point in the night.
So if you want to chance being able to request a patio table, I would go with the 7:15 pm ADR, but know that you're going to have to drag out your meal to make it last long enough.