We have been to both and loved both of them. In fact, we are going back to both this trip.
We have been to Coral Reef twice and it was great both times. In fact, it is my husband's favorite restaurant in WDW. It is a must do for him everytime. The atmosphere is great, and his steak is always perfect. If you like steak, you can't lose. And, as far as I know, there isn't any shellfish on the menu, just fish, chicken, pork and steak.
We went to Cape May for the first time last year. I loved it, my husband liked it. (he wasn't that hungry so didn't eat much) I liked how there was a good balance of seafood and regular food. I loved the crab legs, but there was lots more to choose from.