I think most of the reviews would indicate that Le Cellier is the most liked at least on these boards but I think it really depends on what kind of food and atmosphere you are looking for. I personally don't like German food (can't even stand the smell of saurkraut) so the choice for me is easy but I always thought the atmosphere at Biergarten would be worth experiencing at least once.
If you have want entertainment I would go to Biergarten. (My children love it), but the food is not the greatest. If you want great food and a more sedate meal I would go with Le Cellier. If you have young children Biergarten is a blast.