Because you are very advanced in math, you need to check the course offerings in math and CS to be sure that each school has enough higher level offerings to keep you interested. This may include graduate level offerings in math and theoretical CS.
Liberal arts colleges seem to be strongly advocated on these forums, but you need to choose carefully in this respect; as undergraduate-focused schools which strive to keep class sizes small at lower levels, many have fewer higher level offerings and no graduate level offerings.