The biggest difference is the controls as was mentioned. If you are a skilled enough welder to try to perfect your weld by adjusting and AMP or two then the miller gives you that ability whereas the Hobart just has fixed settings. As far as welding aluminum, they can all potentially do it, you need a different gas and the spool gun should be used with any of them. That is because the aluminum wire will kink easily and going all the way through like the steel wire does will create more opportunity for the kinks.
