I have a backpack with hydration bladder (3L) that I sometimes use for commuting. I go back and forth between that (easy of just hopping on and going, huge capacity) with a smaller bag in my folding basket and waterbottles (not on my back so less sweat until it gets super hot when it doesn't matter, fits in my locker unlike the rigid internally framed backpack, just like storing bottles in the fridge better than bladder, easier to clean). Right now bottles and small bag are winning, but that might change when summer comes.