I've been a welder for 25 years. I've used all different sizes of Miller's, Airco's, Lincoln's, Hobart's and a sweet purple Thermadyne.
http://www.thermadyne.com/
I ran Aluminum MIG with a Cobra-matic and a Thermadyne powersource as a production welder for 3 years. Never ever had a problem with it and that machine was the smooooothest heat source I've ever used to this day.
I will add all the commercial machines I used were 480V 3-phase. Unless you're near a commercial zone, that won't available for you. Plus it would be a fortune to get it plumbed in.
For TIG welding, my favorite was a Lincoln Ideal-Arc, I used it for 12 years. For steel MIG, my favorite was a Miller...
Let me add this: I have a wee little Lincoln 110V SP-135 MIG welder for home garage use. I use .023 hardwire with a bottle of 75/25 gas. That'll max out with a nice weld on 1/8" steel. But, if you want to do body work on sheet metal, that little sucker will dial in real sweet and I'll bet you could weld around a pencil with it. You can't beat it for sheet metal work.
I also have a roll of .030 innershield wire that doesn't use any shielding gas. That'll max out on 3/16" steel. If you have a torch and can pre-heat your job, you can weld 1/4" with it but you're pushing it. (Never use them with a smaller extension cord.)
Little 110V machines are not for welding bumpers and heavier structural jobs and they can cost over $500.00 bucks.
Take Rock Lizards advice and buy at least a 220V MIG machine for versatitity. -Unless you are
only going to weld thin sheet metal. Otherwise, you will never be happy with the money you've spent.
That's my .02 worth
Landy