Originally Posted by
San Rensho
Neither. a shoulder bag with a very long strap so that when you are on the bicycle, the bag is below your waist. This keeps the center of gravity very low, so the load doesn't flop around like it does with a backpack, and also keeps your back cooler since the bag is hanging off your waist and not stuck to your back.
I've tried that, and had the strap long enough to hang the bag behind my butt. But, it always wanted to swing around to the front, where it would get knocked around by my legs. It was especially bad on the CAAD8, and the Bad Boy isn't exactly an upright-posture bike either, so a long-hanging bag still had a tendency to swing around the front.
Maybe you've got yours worn differently so it doesn't swing around, but whatever I was doing, the long strap wasn't working like I wanted. That's why I was looking for something to stay in one place no matter what.