What happens is that the gas torch is not quite as hot as the arc on a Mig, you therefore compensate by going slower/heating longer, which creates more warpage.
IMHO, almost anything you can do with a Mig, you can do with gas. But you can do a lot more with gas, like weld upside down, braze, cut etc . . . Downside is that getting "good enough" welds is a lot harder with gas. However, the difference in the level of skill required is much smaller if you want to achieve top quality "pressure grade" welds.
I think that for most hobbyists doing routine stuff a Mig is the way to go.
Michel
QUOTE(bondo @ May 18 2006, 08:10 AM)
Plasma cutters can cut aluminum.. beat that!
Gas welding drawbacks: Hard as hell to do, slow
Gas welding benefits: Better if you need to work the welds afterwards (john kelly flares, etc.)
I've read that gas welding causes less warping because it's not as hot, but that's the exact opposite of my experience, probably because I'm not very good at it. I tried gas welding sheet metal on my Mustang, and it warped all to hell before I even got it hot enough to weld. I gave up and bought a mig.