Things that I would take into consideration:
Character wise... You would be meeting three characters that don't overlap with your other meals at 1900 Park- Mary Poppins, Mad Hatter, and Alice (Pooh and Tigger will be seen when you eat at Crystal Palace). At Cape May you will be meeting Donald, Minnie, and Goofy in their beach outfits which is very cute. Based on the rest of your dining plan, you will meet members of the Fab 5 a lot. Which characters are more important to your family?
Location wise... We try not to travel all over the place just for a meal. I would take into account where you are planning on going that day. If going to MK, I would lean towards 1900 Park. If going to Epcot or HS, would lean towards Cape May.
Food wise... We really love both locations and have only had positive experiences at each restaurant. Both restaurants have options that the other doesn't have (omelette station and strawberry soup at 1900 Park for example) but they also both have the same standards (mickey waffles!!)
I would probably lean towards Cape May just so you can try a new restaurant. However, if the characters at 1900 Park are more appealing to you, definitely go there!