I haul everything in a large messenger bag. My bike handles better, performs better in the wind, and my upper body core muscles get a mild workout.

I'll even stop in on my way home on Friday and throw 12 longnecks and a bottle of wine in there in addition to clothes and papers for work.

My commute ranges from 10 to 33 miles r/t. I have not ridden with a back pack, but I imagine that it would sway a lot in addition to the sweat factor.

The panniers stay on my old hybrid set up for shopping.