We've done both breakfast and lunch, and we prefer lunch. DH preferred the food at lunch - he wasn't too impressed with the breakfast. I, however, loved the stuffed French toast.
But we're really not morning people. We're doing well to get to the parks by opening - much less earlier for an early-morning ADR. So, we really do prefer lunch.
W/ your girls, I would do either breakfast or lunch. Cinderella is in the lobby for breakfast, lunch, and dinner, but the other princesses only circulate among the tables for breakfast and lunch. At dinner, the Fairy Godmother, Suzy, and Perla are there, but I don't think they go from table to table. Children also get wands (girls) and swords (boys) and wishing stars at breakfast and lunch - I don't know if they get these things at dinner or not.