I’ve used both, hated both and loved both. I’ve traveled with two messengers for a weekend trip and hiked with one, and I’ve cycled with very heavy backpacks that almost took me down with crosswinds.
I get a sweaty back; so I was carrying a messenger bag this summer and fall. But usually I hate adjusting them (even with the cross-strap) and the Messenger Bag Should Sloop (where you’re just bent from those things). I used to like that carrying a messenger bag identified me as “a cyclist.” But, for one, that’s not really true. Just as everyone with a backpack is not a backpacker, traveler or vagabond, not everyone with a messenger bag is a cyclist. Secondly, I don’t want to be identified by my favorite mode of transportation. I do also walk and take transit a lot. Plus, well, if we want everyone to cycle, the cyclist/non-cyclist distinction is counterproductive.
I do notice that I over-pack with backpacks. Right now I have 17 pens and four Moleskines on me. No kidding. Add work papers, dissertation drafts, a 40 oz water bottle, lunchtime book and other junk, and it’s a lot more weight on my back. Sweating is not usually a worry this time of year, but I think my high-riding daypack can get in the way of my helmet a little.
Lately, I’ve been throwing my stuff into an old totebag and strapping it to my rack. I do feel like a sucker with a bag on and an empty rack. I call it my Bike Bindle. I’ll have to do a post about that.