I have eaten at both San Angel and Le Cellier....
My vote is Le Cellier hands down! San Angel is fine, it's a pretty atmosphere inside the temple, but I think the food is way overpriced for the quality. And you can just go in the temple and look around without eating at this restaurant.
Both my husband and I LOVE Le Cellier. We went there last summer and the servers were wonderful and the food was wonderful quality. Definitely worth the price. And we just happened to mention to our server that we were celebrating our anniversary that trip, and she surprised us with a yummy chocolate cake with "Happy 2nd Anniversary" written on the plate. We had a wonderful experience there....I would highly recommend it!