Congratulations on two great acceptances. Brown/RISD is a fairly new program (only 4 years old I believe) and is a 5 year UG program, right? The cost, therefore, must be factored over the longer haul, if cost is of concern. In the past, the RISD kids bond very tightly in the Foundation year. I'm not sure how well they do when they leave RISD and have to blend into the Brown world--those students have also made their friends, one would think, freshman year. Because each school is amazing, and because this program is so new, can you speak to some students who have been in it to get their reactions to how it works for them. Would they do it over if they could choose? Was there much attrition?
As for CMU, they do have amazing comp sci courses as well as an amazing art school. Have you checked their UG catalog to see if you would be able to take enough courses in your preferred area of animation and also get into comp sci courses easily?
Best of luck in your decision.