I had a crumpler messenger bag that was perfect for a laptop, change of clothes, lunch, and a small electrician's tool kit. I ended up giving that to a coworker for his motorcycle and then he died.
My experience is that the timbuk2 (medium) is better with a small load and gets cumbersome when its fully loaded. My chrome metro's the exact opposite, it feels kind of loose with my usual load of lunch, work clothes, and pair of sneakers.
But every couple of days when I really need to stuff it, it feels great on my back. If I were you and I don't plan on carrying around too much, the citizen stuffed would work pretty well.

I got my chrome in all white vinyl, which is basically two thick liner type layers instead of the usual liner and nylon. The advantage is that it's completely slick and doesn't absorb any water or sweat at all. The disadvantage is that it's completely slick and doesn't absorb any water or sweat at all.