If your going to be welding aluminum the Thermal arc offers AC frequency control that the Lincoln does not.
The Thermal Arc is smaller (due to being an inverter) and easier to move--or steal. The inverter may also allow for more flexability in power draw if your hooking up at home.
The Lincoln is no dog... Great machine, great support.
Miller also has a Dynasty 200, but that may be a little more spendy, you'll have to check.
Esab also makes little inverters..
Visit your local suppliers and find out about warrenty work, who can/will fix what.
dbeaman,
I have a Precision Tig 185 and it works great on alum.. You can adjust the wave balance in AC or put it in auto balance. Plus the pulser helps make some really nice welds on thin alum. All in all I think it's a really nice machine but it does weigh in at over 200 Lbs. so portable it's not.