The bigger MIG welders are nice, like the Miller 210, or Lincoln 215. They have all the capability of the smaller 110V machines plus they give you the ability to weld thicker metals as well. They also give more adjustability of the parameters like wire feed speed and voltage so you can fine tune the arc for the best weld possible. The only problem is the price. Expect to spend $1000 or more for a good 220V MIG welder. You can get a smaller 110V MIG for about $450 (Lincoln SP135). The 110V machines are probably all you need for anything automotive.
Check out
www.usaweld.com. This company, called HTP, is a smaller company than Lincoln or Miller, but they seem to have a quality product, and I hear their customer service is great. You can even try a welder for 90 days, and if you don't like it, they'll take it back no questions asked. Kinda cool. I plan to buy a TIG welder from then someday...
If you really want to get serious, you can check out the Lincoln Power Mig series of welders. These are capable of MIG, TIG, Flux-core, and Stick. You can hook up a foot pedal to control amperage for TIG, and you can even hook up a spool gun for MIG aluminum. The Power Migs can do a Pulsed MIG process that greatly helps with sheet metal and out-of-position welding. These machines are awesome, but awesomeness comes at a price $2500-$3500. A crap load of money, but one helluva welder.
