I was a transfer and went through informal. Though my school is large student-body wise, the Greek system wasn't that big so pledging wasn't very hard. However, even at bigger schools like UM, I'm surprised more sororities don't seek out sophomores with excellent grades. Most college kids need time to adjust to a big life change like going to college (especially a big one like Michigan) and a soph with a proven academic record and desire to be involved seems like a big advantage rather than a wide-eyed scared freshman who may not realize what she's getting involved in.