I'll take the opposite view and vote for the Dolphin. 2 Reasons:
1. I've never waited behind more than 2 people at the Dolphin. At the CCC, I've had to wait behind 15 people or more. If you get there just as a busload of people gets there, it can get pretty lengthy.
2. The dolphin fits into the day better. We go to Epcot or MGM, do a few things or eat then walk or boat over to the dolphin and get the car. Same with the return. We return the car then head to a park immediately. We don't have to wait on a shuttle. It feels more like we control the time.
While you don't get to choose your car at the dolphin, I've gotten a free upgrade (without a coupon) every single time. I don't know why, but I always book compact and get a full size or bigger.
Dolphin for me!