I have Chrome Citizen and Metropolis messenger bags and an Ivan rolltop backpack. For any serious amount of weight the backpack is the most comfortable. For my regular commute I carry the Citizen mess bag, though. It's a good compromise on size, convenience (I can get into it without taking it off), and comfort. I'm 5'7" and I find the Metropolis to be too huge for my frame unless I have it really stuffed. (bulk, not weight) If the weather is really wet, though, I use the rolltop, it has yet to let anything get wet and I've worn it through some severe rain.