I also think it is a personal preference - I prefer the panniers, even the times I only use 1. I sweat alot, so it makes more sense for me not to have something on my back. I tried the messenger bag for a while and that was ok, except for the sweaty back and the occassional item that would not sit right and poke me in the back. The only glitch I am still working out is how to safely carry a laptop in my Ortlieb Back Roller panniers. I am in the process of researching this but I am still nervous since the bike takes the road jarring, where as a messenger bag or pack back would have the body to act as a shock absorber.