IF your going to get one, IMHO< I think a non-military looking one is best for a BOB. If your already at your BO Location then camo is great but I think just plain black is a wise move. Mine on the outside looks like a camping bag. Less attention, less 'tactical'. is probably less interesting to an observer.
I believe that if SHTF and it's really bad out it doesn't matter if your bag has hello kitty on it, if someone sees it they will try to take it. That's when a couple JHPs will come in handy.