I'm looking to buy a backpack style laptop bag with a single strap since they appear to a lot less cumbersome than the brief-case style I've been using. Do any of you have a particular bag you like and why? Ideally I'd be able to put my 15" or 17" macbook without any risk or bag modification. My current bag has two velcro pads to accomodate a 15" but don't prevent the laptop from sliding up and over the pads at all.