I used to use a back pack but now after utilizing two inexpensive Nashbar panniers for the past six months or so I am reluctant to revert to a backpack unless I am carrying very little. Sometimes I carry upwards of 20 lbs. of necessary items in the panniers so that obviously is not conducive to wearing a pack. Other times I am picking up produce on the way home which the panniers are wonderful for. I suppose it all depends on the individual's comfort level and what they plan on carrying.

Untitled by irishbx4th, on Flickr