MIG is all I haved used, but I have used it on many parts of my Jeeps with great results. The welds are not as pretty as a TIG could make but they are plenty strong. To my understanding, if you want to weld thinner material (sheet metal) a TIG would be better; less warping; no slag. But I have used a MIG to box a frame, fab custom motor mounts and cross members, build a new rear section of body (see my gallery), make tubular and flat bumpers, fab exhaust, repair cracks, build a storage box in place of stock fuel tank, new shock mounts, build an aquarium stand to match my entertainment center... lots o' stuff. I have used it to weld sheet metal to 3/16" thick tube as well - but the sheet does warp when doing that.
There are some combo welders/plasma cutters out there that rock so keep an eye out for those if you plan on lots of fab work. Plasma cutter.... mmmm... must have one day...
Here is the MIG I have: http://www.mylincolnelectric.com/Cat...eet.asp?p=7083
Sent from my "two hands on a keyboard"