My old bag was too long to fit front-to-back in some airlines' overhead compartments, so I want one shorter than that. I value a sturdy, easy-to-use collapsable long handle to drag it around by, and I want the wheelbase to be sturdy as well. It should also be well ballanced on the wheel base - my previous bag had a tendency to fall over forward when standing, which got annoying quickly.
Color doesn't really matter, though something other than black might be refreshing - otherwise I'll decorate it.