There are a couple of backpack threads on here that you should do a search for.
I bought a Jansport "Odyssey 38" backpack (very popular hiking-style backpack...it seems like half my class has one) the day before classes started and I swear it is the best purchase I have ever made. It has tons of room for lugging books to school and back, and lots of compartments. The ultra-padded shoulder straps and hip/chest straps are key for hikes to the parking lot or home.
Satchel/sling bags are a popular option, but they hurt my shoulder when they're loaded down, and I don't think they generally can hold as many books without getting unwieldy.
Using a rolling backpack is a surefire way to look like a huge nerd. I don't care if they're better for your back...you won't ever catch me using one.