We've done both - and we'd choose Cape May Cafe. They do offer very different types of meals, so it depends on what you like. Here are some observations:
Cape May Cafe - Served buffet style with a huge assortment of hot foods, breads/pastries, fruits, yogurts and cereals. The food is fresh and excellent tasting. The characters are Minnie, Goofy and Donald dressed in beach attire. The place is very bright and colorful with tables and booths.
Ohana - Served family style where the server brings a platter of scrambled eggs, link sausage, bacon, breakfast potatoes. A separate server comes out distributing Mickey waffles (sometimes several minutes later which makes my boys cranky waiting for their food). The characters are Mickey, Pluto, Lilo and Stitch dressed in hawaaiin shirts and leis. CMs will hand out instruments and the characters will do a musical parade around the tables.
I much prefer a buffet where I can select from lots of food choices based on what I'm hungry for that morning. I thought the food quality at Ohana was just OK. Cape May Cafe is a must-do for us every trip.