I use both a backpack and a messenger bag, the backpack more often to be honest.

i cannot get a messenger bag as large as I want - to carry my work clothes, my gym kit, running shoes for the gym and shower flips. A little too much for comfort in the messenger bag. If it's just work stuff, then I take the M Bag.

i use the Timbuk2 Especial M Bag, it is wonderful. The Timbuk2 Phoenix backpack.

i tried the Chrome Metropolis and did not like it for one simple reason. It rides over the left shoulder and I prefer a bag on my right shoulder.