Excellent choices.
I have heard great things about all three of these restaurants, but I have only been to Le Cellier and California Grill. I have a tough choice picking my favourite, but here are some things you concider to help make your decision...
1) How much do you like steak? If you're planning on ordering it, I think that Le Cellier's Mushroom fillet mignon surpasses the red meat offerings at Cali Grill. But then again, only a few of the entrées aren't steak.
2) Do you like sushi? The sushi at California grill is excellent, very fresh and tasty.
3) Do the appetizers appeal to you? I think that what the Cali Grill really has in terms of food over Le Cellier are stellar apps. Le Cellier has cheddar cheese soup, duck, mussels, and some things I haven't tried. Cali Grill has fantastic flatbreads, the aforementioned sushi, and...some things I haven't tried but wish I had. Here are the menus.
Le Cellier:
http://www.wdwinfo.com/wdwinfo/dining/diningdetail.cfm?restaurant.ID=137
Cali Grill:
http://www.wdwinfo.com/wdwinfo/dining/diningdetail.cfm?restaurant.ID=105
4) Dessert: The California grill has fancier, more interesting desserts. Le Cellier has superb crème brûlée.
5) Service: The servers at Cali Grill and Le Cellier are excellent, but for different reasons. Service at Cali Grill is professional. The servers at Le Cellier are incredibly friendly.
6) Atmosphere: Le Cellier is a recreation of...a wine cellar. It is actually quite cool and relaxing. California grill is the more romantic of the two, with spectacular views and a slightly quiter dining room.
Any other questions, feel free to ask and I shall answer to the best of my ability.
[EDIT: I forgot to stress that for any of these restaurants you'll want to make your reservation ASAP]