I'd been commuting with my trusty, old LL Bean backpack for about a month after my timbuk2 messenger bag was deemed too small and uncomfortable for my 27 mile RT commute. I'd had the LL Bean backpack since the 7th grade (I've been out of college for a year now ) so it was definitely bulletproof. Most of the zippers were toast and the fabric was wearing thin, not to mention it wasn't the least bit waterproof and definitely wasn't built for cycling as it was pretty uncomfortable.
I opted for another Timbuk2 bag as I liked my messenger's build quality and organization but wanted a 2 strap, so I went for their medium Hemlock (also because I got it on clearance for $59). This thing is pretty awesome. It's gigantic, and I haven't been able to fill it to maximum capacity. I can barely feel the weight and the straps are very comfortable. It's a simple pack, so one main giant compartment and a few organizational pockets in the front pouch. The roll top will be useful once I have some extra stuff I want to carry home. As far as breathability, I'm not really sure, as I get sweaty with or without a backpack during my commute.
Personally, if I had a bunch of money to drop, I would've gone with the Mission Workshop Vandal, but at $269, it's a nice chunk of change. I guess my choices are pretty close to being within the hipster crowd, but I guarantee you I commute on a CX bike and am building a drop-bar MTB, and both of them have black tires ......