There is no "best" backpack, there is only best if the pack fits you comfortably, will handle what you carry without problems, will allow air to pass between the pack and the back. Personally I don't like backpacks, but for short commutes their fine. Bike shops sometimes sell backpacks for cycling but unless they have some sort of system for raising the pack off the back a bit for air to get between the pack and your back then it doesn't matter if you get it from a cycling store or a camping store.