art portfolios

They are looking for the promise of future success, and the "evidence" for that will differ with each professor sitting on the admissions committee.
Thus, for any major (not just art), the aspiring student should apply to schools containing faculty with whom you would like to study (and who would therefore most likely like to work with you--and thus vote to admit you to their program)

A bit of free advice from a retlired professor who has served on many admission committees.