Back in 2007 I reviewed the Spire Torq backpack for the PowerPage. What I didn't realize at the time was that the Torq would become my favorite bag for my 15-inch MacBook Pro. Since writing that review I've been using the Torq as my primary bag for about three years or so -- and it's excellent.
I generally prefer a backpack over a messenger bag and have for the last several years. Backpacks are simply more practical when traveling as they stay put and keep your hands free. The Torq is an excellent choice because it's deceptively spacious.
When you only need to schlep your MacBook and the standard complement of accessories the Torq packs down quite small via the four tightening straps on the sides. However, it expands easily into a large-ish weekender with enough room for all of your various gadgets and enough clothes for three full days.
Spire updated the Torq backpack in 2009 and it's even better than the original. It's constructed of 100% Cordura Velocity nylon and heavy-duty #10 YKK zippers. There's now even more padding in the shoulder straps and the two mesh side pockets can accomodate everything from water bottles to smartphones and snacks. They even improved the key hook inside the outer pocket -- now that's attention to detail. Spire also switched the velcro on the Boot -- the beefy notebook sleeve that's included -- so the hook part is now on the body of the bag preventing fuzzing.
My Torq has been time tested and has hundreds of thousands of miles on it including several cross country and international trips. It's my go-to bag for short and long trips alike and it's worthy of your consideration if you're in the market for a new bag.