I vote for the Ortleib Downtown...get the QL-3 mount option...it is truly a thing of beauty to set the bag onto the catch points and know it's held on. Removing the bag is just like picking it up off the desk...seemless.

The Bag itself has a laptop divider within, a key strap, little interior velcro pouches, a nice removable shoulder strap and it looks great in the office (mine is black). Oh, and it stands up vertically unlike other bags I've owned...makes it nicer to load/unload etc.