I have a small day pack with the chest strap, keeps the bag thight, and dosent wiggle or bounce around when im really pushing it.
I have used a timbuk2 bag before, and it was nice, however i can fit alot more in my daypack, and imho, it looks better. However! not all daypacks are waterproof, and the timbuk2 bag i had, was waterproof, if i had to carry a laptop to work, i would have used the timbuk2.