I have stayed at both, and enjoyed both, but they are very different experiences.
If you want a trip that still feels very Disney even though you aren’t going to the parks, BLT would be my choice. You will have a clear view of the MK fireworks from your resort, occasionally hear the train or steamboat, and feel closer to the action. It is also convenient for traveling to other resorts, since you can simply take a short walk to MK and catch a bus going anywhere you want to go.
If you would like a trip where you can sometimes forget you are at Disney, or even in Florida, then CC is the better choice, in my opinion. I have stayed at WL/BRV/CC many times for resort only trips. I like that I don’t have all the hustle and bustle right on my doorstep. The theming is so good that it’s easy to feel like you are far away from one of the world’s busiest theme parks. I can relax there and not feel like I am missing out on the parks at all.
Either one is an excellent choice. It just depends on what you want out of the trip.