I've been searching for the perfect backpack as well. I decided on a Bagaboo workhorse. All the backpacks I wore had serious blindspots, and I wasn't sure I was ok with that. Obviously when you have a large load, 2 straps are better than 1, but often may not be necessary. The workhorse has a strap that can swing around and act as a 2nd strap similar to a backpack.

I'm not a messenger, nor do I ride any sort of ss/fg/track bikes but I live car free (in Atlanta) and a good pack is very important to me. I just got it a while ago, and I think I'll post a review on it. I was originally trying to decide between a seagull or a reload backpack but ended up with the bagaboo outta left field. There's just not that much info out there on any of these bags, especially the much less popular backpacks, so I thought it may be valuable to post a concise review. I know a lot of you folks live in places with a lot of cyclists, but here we are few and far between, and finding one of these bags to try on is a pain.