Good thinking, Twicer.
The size and prestige of one’s undergraduate institution – even for someone who intends to get a PhD and work in academic mathematics – are less important than what has been stated in this thread. It is far more important in my opinion to find an institution that is a good fit, where the student will be happy and thrive. Mathematically you can do absolutely no wrong with either of those departments, so pick whichever school makes most sense and feels most like home to kiddo and family.