I have a Seagull bag and a Timbuk2 bag. The Seagull rides infinitely better; no questions about it.
However, my ride is only [at most] an hour or two a day, and the rest of the time my bag isn't a messenger bag - it is my work bag. The Timbuk2 is far better at this part of the day [8-10 hours]. I have a beautiful Seagull bag sitting in my closet and I really prefer my far less expensive Timbuk2 for most days.