Boma is at AKL, Kona is at the Poly.
'Ohana is a lot of food (all you care to eat) served family style. Aside from the grilled meat, it has some pan-Asian touches to tie it to the Polynesian theme of the resort and the restaurant. There is a separate kids' menu if they do not like what is on offer, but you may have to ask a CM. There are some hula and coconut racing distractions during the meal, and the restaurant looks out over the Seven Seas Lagoon, and the MK fireworks, if you're there at the right time.
Kona has a standard menu, not all-you-care-to-eat, and also have the benefit of access to freshly made sushi, if that's what you're in the mood for. There is no view out, except into the lobby, but Kona is usually less heavily attended than 'Ohana.
Both are very good. We're 2 for 2 with Kona and 3 for 4 with 'Ohana in terms of having good meals. 'Ohana is much more of a show with a strong theme, but Kona puts out good food and lets you be a little more picky about what, exactly you eat. They are very different restaurants, so it really comes down to what you want to eat, and how far out you are making a dinner reservation, as 'Ohana tends to fill up.