Messenger Bag vs. Back Pack

[GLC1968]

I've always been a fan of the backpack for the secure feeling and balance. I have a Timbuk2 laptop backpack that has a channel that runs between the pads on my back. When I'm riding, I tip my head down for a second and air rushes down that channel and cools me off...very neat! If you are in a very aero position on the bike, the center of gravity is a little high and makes it feel precarious. It worked for me with bars level with my saddle (even when I was in the drops).

That said, I've lately been using a messenger bag because it's much bigger (and I don't carry my laptop so much anymore). It's easy to get in and out of (like at the grocery store) and it holds a ton of stuff. Mine's a Timbuk2 large which is really too big for my frame, but with the retainer strap, it sits still and remains comfy. I also find that it actually works better when it's got some weight in it.

I'm no help because at this point, I'm torn. Of course, I haven't ridden in the heat with a messenger bag...or for longer rides...so technically, the jury's still out.

Oh, and I'm editing to add that I prefer the bags over panniers because I switch bikes a lot. This gives me much more flexibility (as a couple of my bikes don't have a rack or even mounts to add one). If I only had one bike that I rode, I would likely opt for the rack and panniers.