Those messenger style bags, in my opinion, put too much weight to one side of your body which is not cool when riding - they just hurt after a while. I bought a Deuter 'race x air' backpack. It comes with a water pack thing-a ma-jig, which I actually took out, but hold onto in case I want it. What I love about this back is that there is a taut, but springy mesh like back rest that rests against the back, with the actual bag part not touching your back , so you arrive at the end of your commute with a nice dry back instead of a sweaty one - this is an EXCELLENT feature. Also this allows for the backrest area never to be lumpy due to the contents of the bag - that bag part never touches your back. So the support and comfort of this bag is second to none in my opinion. The drawback is that this bag does not hold a whole lot. That said, there are various deuter models, my model is not meant to carry a whole lot - still does the trick though. Btw, almost forgot, the straps are also mesh so that you stay dry. Don't really need the padding because there are 2 straps , one around the chest, the other around the waist that really distribute the weight nicely - way better for your back than those messenger bags!