There's really no shame in applying more than one place, I'm sure that the admissions people know that you've applied multiple places and they probably know that multiple places are courting you for admission. If you scheduled a visit and then flaked out, that would be unprofessional and also not in your best interest. I think as long as you explain the situation and make sure they know that it doesn't mean you aren't interested or grateful for the offer, then it's no biggie. As far as choosing which one to go to, if you've already scheduled one I would say stick with that, if you haven't scheduled either yet, maybe the interview is a bit more important.