Timbuk2 bags suck...the strap on a seagull is 100x more comfortable. Adjustments to strap length can be done simply by tugging on the end of the strap and loosened by pulling on a little piece of strap that hangs off the buckle. Super easy. Also, it comes standard w/ a stabilizer strap that I use all the time. This keeps the bag from swaying with small or large loads.

The only problem w/ the seagull bag is that, when you are carrying super small loads (a notebook and a u-lock for example), you have to pull the strap so tight that you then have this d-ring dangling around. But that's not even a big deal b/c you can just tuck it behind the main strap