Well, it really depends on your budget, food preference, atmosphere you desire. What are you wanting?
If you are looking for something Fun - Hoop de doo, Whispering Canyon Cafe, The Spirit of Aloha Luau.
You could also eat at Cinderella's Royal Table, which is where I ate my b-day dinner!!! It was wonderful!!!!!
If your party doesn't mind eating later in the evening you could possibly arrange your ADR to be able to see the fireworks.
Or you could book the Fantasmic dinner package at MGM.
We also enjoy Coral Reef, my DS loved the tank - though I doubt a party of that size would all be at the same table - you'd be close though maybe.
There are some good steak places, again this will depend on budget - We like the Yachtsman, the Concourse is also good.
You could also do a Character dinner.
You can look on Allears at menu's and that may help you to decide. I'd say go look at the menu's, decide on a couple that look good, then ask for reviews on those.
I'd be a little wary of Boma though, while it is very good, my DS (who is an adventurous eater) did NOT like it. The foods and flavors are different, they are African and may not be the best choice for the entire party.
Also, as a side note, you can call dining at your resort or central dining and order a b-day cake, cinderella slipper dessert, choc. cov. strawberries....... etc. I had the slipper for my b-day and it was fantastic ~~ Keep in mind though that it must be ordered in advance and pre-paid, you CANNOT get it off the menu.
Good Luck!!