The ATR42 and ATR72 both board from the rear as there is a cargo compartment right behind the cockpit and in front of the main cabin. Row one does have the most leg room, but if you have wide hips don't sit there as it has the unmovable arm rests due to the tray tables. Row one is also the only exit row on the aircraft. In Miami all boardings are via bus, so no prboarding is usually done.