How long has it been since you got your undergrad degree? I also come from a liberal arts background (a weird double major that combined studio art/humanities/foreign language), but have worked a few years professionally as a graphic designer. I'm going to VCU in the fall for their two-year MFA. I think it comes down to your timeline and finances. If you're fresh out of undergrad and not worried about the finances, the post-bacc programs might not be a bad way to go. You could get a really great foundation, but then have more options to apply again to 2-year programs, including the school where you're doing the post-bacc and others. You'd also possibly be a little more clear about what you want in an MFA program—more focus on theory, discourse and experimental approaches, or a focus on more traditional approaches; rigid curriculum or loose framework for independent exploration.
I've heard good things about the MICA post-bacc—I interviewed there for the two-year program and was given a tour by a current student who had done the post-bacc before moving into the MFA. He also had a liberal arts undergrad degree. He had nothing but good things to say about both programs. It does seem like the post-bacc students are kept separate from the MFA students to a certain degree, kind of living in between the undergrad and grad students, which I guess makes sense. The facilities are amazing there, as I'm sure you saw. Another benefit to the MICA program is that it seems well connected to the east coast design scene. Ellen Lupton is a co-director of the MFA program, and she keeps the students involved in the latest discourse, frequently involving them in publication and curatorial projects. I didn't look much into the programs at SAIC, Pratt, and CCA, so I wouldn't be able to make much comparison there.
The upside to a three-year program like CCA (or RISD or Yale or a provisional year at VCU) is that there would be continuity between your foundation year and the final two years. You would already have your community of other students and professors at the end of your first year, and you would move seamlessly into the MFA. The downside to the post-baccs at MICA and SAIC is there's no guarantee that you'd be admitted into their MFA programs if you wanted to stay, as far as I understand. So it's almost like you'd be putting effort and money into that foundational year without the security that you could continue on in the MFA. I would certainly hope you would have a leg up at that point, though.
Good luck with your decision!