Speaking from personal experience, I strongly suggest going with either a heavy duty laptop backpack or a rolling backpack. I started off with a messenger style bag that came with my laptop. While a laptop is in it, it is simply too heavy to carry far, no matter how I wear it - add a single case book to the bag, and it's a very unpleasant experience, even if it fits with no problems.
For a while I tried carrying my books seperately in a regular backpack, and my laptop in the laptop case - still too heavy and it didn't work well with the number of books I needed to take home. Eventually the zipper of my backpack unzipped itself in the middle of a crosswalk, due to the weight, and it inverted, dumping case books on the street :-P Not too easy to pick them up and sort it out, especially while trying to hang on to my laptop.
After that I moved on to a Victorinox laptop backpack (the Sahara model, or something like that). I've been pretty happy with that overall for the year that I've had it - it's quite durable, enough room for 4 casebooks and a few smaller ones, folders, etc, and the usual bells and whistles. The only drawback is that brand is fairly expensive ($130 for the backpack?), and carrying more than a couple books in it for a mile or two per day gets a bit rough on the back.
More recently (with more books I need to haul around) I went for a Jansport rolling laptop backpack. They had a couple models at the store I went to, and I opted for the larger one. It's got at least as much space as my Victorinox backpack, and rolls very nicely, though going down steep hills has taken some practice. It's also nice to have it useable as a backpack when rolling isn't an option - the straps don't look as comfortable as the Victorinox, but they are padded at least. It cost about $80, and the smaller one was $60. While I haven't had it long enough to attest to it's durability, my friend got the same one several months ago and is very pleased. Given how many rolling laptop cases she's gone through in the past 10 months (6!) I consider her an expert on the subject
So I'd recommend a roller unless it's impractical due to the terrain, in which case I'd recommend a heavy duty laptop backpack that will distribute the weight on both shoulders. Ideally I'd like my Victorinox to sprout wheels and a handle while keeping its very comfortable back and straps