Hmm, both are actually my favorite dinner restaurants.
Ohana pros:
-Family style, you don't have to get up to get your food.
-Since you will be at MK, this will be a lot easier to get to. Just hop on the monorail.
-Amazing service and food
-Entertainment for kids
Boma pros:
-Buffet style, there's more choices, but you have to get up and go get it yourself.
-AKL is an amazing resort to walk around while waiting for a table, or after your meal.
-Amazing food and service
But I guess I would have to go with Boma.