Panniers and a rack, totally. I'm never going back to wearing a backpack on a bike except maybe a small Camelbak when mountain biking. The wind resistance is negligible for me. Unhooking is easy. I need to carry too much stuff on my commute carry it all on my back. I actually have rear and front waterproof panniers. I can run errands, go shopping, go pickup stuff or drop off something at UPS, whatever. For me commuting means utility cycling too. I would love to commute on a Big Dummy but it won't fit in many elevators.