If I had to choose, it would be Cape May Cafe. Both are a great character meal, but are very different. So it depends on what you are looking for.
Cape May Cafe - has a fabulous selection of hot/cold foods at the buffet. The atmosphere is very fresh and open. They have both booths and tables to sit at. The characters are Minnie, Goofy and Donald all dressed in beach attire. The tables have a white butcher paper on them that the kids can color on the table cloths with crayons. This place is great if you are heading to Epcot or DHS that day.
1900 Park Fare - has a smaller buffet selection. The dining room is a bit more formal/elegant feeling. The characters are Mary Poppins, Alice, Mad Hatter, Pooh and Tigger. Mad Hatter is so hilarious -- it's worth it just to see him!! This place is great if you are heading to MK that day, just hop on the monorail.