There are fervant fans of both restaurants, but as you can well-imagine, the fans of Coral Reef are concentrated among folks who like seafood, while the fans of Le Cellier love steak. Both restaurants are good, but not great, IMHO.
Coral Reef used to be much better, among the best at WDW, but that was about 15 years ago. Since then, some incredible seafood restaurants have opened, including Flying Fish (which I do NOT recommend with small children -- it's always been a specific problem I've noted there). By the same token, Coral Reef is still a wonderful dining experience, with great food, fantastical desserts, and a great view of the huge Living Seas aquarium, from every seat in the restaurant, sure to be a wonder to the little ones. It is pricey, but then what isn't at WDW?
Le Cellier is extremely popular, since the cuisine is much more generally appreciated, being, basically steaks! There are better steaks on-property, but Le Cellier's more costly steaks are consistently excellent. Sometimes the less costly steaks available at Le Cellier I wouldn't serve to my cat. Beyond the stakes, most of the food is especially yummy, especially the cheddar cheese soup, and the stacked tomato appetizer. It's family friendly, as well.