As someone who has used both, I can say this with utmost conviction: messenger bags will **** up your shoulder and back over the long haul. I use a Chrome Pawn now exclusively, which makes my Seagull sad and introspective. But my left shoulder thanks me everyday for it. On a sidenote, I have slight, left-leaning slouch now. I'm almost positive that's it from using mess bags for so long, and my old chiropractor said it's a legit reason to pin my slouch on. Not THE reason according to him, but definitely something that could have contributed, and probably did.