Business casual is always a safe option. Sure, don't wear uncomfortable clothes (especially shoes), but I don't see a reason to assume business casual would be uncomfortable. I wore grey pants, button-up shirt, a business casual jacket and flats. I also took off my piercings. Will a school ban anyone from the visit for wearing sweat pants and piercings? No. Probably no one would make any comment about that. However, wearing unquestionably appropriate clothes can make you feel more confident. Remember profs are just people and some of them won't care at all, but some might think (or unconsciusly assume) that more professionally looking students are more serious and responsible.