To me one of the most important thing was happy staff. I want continuity of care for my baby so he can get attached to his carers and they won't change every year.
The other thing was communication between the center and the parents.
Nice to have is a center that cook the food for lunch themselves (as opposed to get it delivered).
Maybe a good place to start is your MCH center. They can give you recommendations of the better centers next to you.