I love the practicality and reflectivity of my custom Timbuk2 messenger bag, but it doesn't hold much and isn't comfortable while cycling, especially on any day over 60F. My Ortlieb back roller classic panniers are huge, easily and quickly attached or removed, but they don't "carry" so well off the bike. If I could do it over -- I would have a backpack/pannier combination (there are quite a few nice ones out now).