What he said.

The Mini and Citizen are good if you only carry a set amount of stuff every day.

If you need to carry groceries or other stuff, picked up along the way, they are too small.

The Metro is about right for everyday use with a bit of room left over for anything additional you need to add in the course of daily events.

An over stuffed messenger bag is not all that comfortable on the back. It's better to have some extra bag so that it conforms to your back comfortably, instead of riding like a bag full of bowling balls.