Here's my take on both:
Cape May: It's a smaller restaurant, so you'll have less wait time between characters. This place features Goofy, Chip and Dale dressed in beach wear. They travel from table to table, but it can be quiet a while before any one of them gets around. Minnie simply greets guests as they enter the restaurant. The food is pretty good, in my opinion. I love alot of fresh fruit for breakfast, and they have LOTS of it (grapes, cantaloupe, melon, etc). They also serve pancakes, mickey waffles, and lots of "kid" cereals. This place has a very relaxed atmosphere.
1900: Bigger buffet that features made-to-order omelets (yummy!). It's a larger restaurant, and also more crowded. I found that the buffet line moved very, very slowly here but I was really pleased with the selection of food. The characters are from Alice in Wonderland and Peter Pan (at least when we were there). As I recall, we saw Alice, the Mad Hatter, Peter Pan, Gepetto, Mary Poppins and one or two others. The characters moved really spent alot of time interacting with everyone, not just the kids.
In short, both places are really enjoyable.