Le Cellier is better bang for your Dining Plan buck, since the elimination of the appetizers. The food is very good and the atmosphere is nice, we always enjoy eating there.
California Grill is amazing, we try to eat here once every trip, but we don't do the dining plan and order what we want. California Grill is one the best dining experiences available at WDW it is superb. Dining here is an event, some of the best foods are the appetizers and sushi. We dined here with a couple, who was on the dining plan and with wine and appetizers their bill was over $150. Our bill was $250 (the wine was the same price) so our bill was $100 more, they paid more that for the 2 dining credits per person on the dining plan.
So IMHO you cant go wrong with either, but if you are trying to get the most bang for your buck, Le Cellier is the better choice.
If you want a fantastic dining experience and don't mind paying extra, then CG is the way to go.