I would use MIG over stick any day
I didn't mean to confuse folks yesterday when I mentioned stick. Pretty much the only reason I mentioned it is because it's probably one of the simplistic processes for welding, all you need is a rod, no gasses to worry, and you can find stick welders inexpensive, nice ones tend to fall off the turnip truck regularly as nobody wants them. I tend to use stick for heavy and/or outdoor work where it's rusted and/or has paint as cellulose stick can burn through that. For all else I can clean I would use 7018. I bought a small stick welder that burns any rod I have thrown at it. Great machine, but cost $600. Will do lift-tig also, and uses a pedal, but no HF start, so all you have is lift-tig, not bad for auto work as HF messes with modern computers in the cars. I have a 2nd tig machine with HF that I use for most everything tig.
That said, they did use stick welding on body panels for a number of years, and I think it would work just fine once you got used to it. As I said, I would use the smallest fast-freeze rod like 6010/6011 (the later runs on most any welder, AC or DC), or low amps with 6013, originally developed for thin sheet work. I like to run stick though, so that's me. Anything clean would be tig'd. You could find a stick welder on craigslist for like $50, get some 1/16" 6013 (not hard to start an arc, actually very easy) and you could do whatever you needed. I wouldn't underestimate the power of stick for the cost. And it's used on most heavy industrial machinery and trailers.
I would be surprised if you found anyone stick welding in a body shop these days, maybe 1 in 500, if that. I would guess the majority would be using mig, some would be using tig, but tig would b in the minority being used by specialty shops. Those 2 processes would pretty much dominate the body shop sector.
If I had mig, I would use it before stick, and if someone else has it and can use it competently, mig is faaaasssssst.
On any body work I would do, I would most likely clean the metal really well and tig it. quiet, smokeless for the most part, and just an awesome process. I don't have to weld this stuff for a living though, so as a hobbyist, my time and choice is more flexible. The majority of body shops will be using mig, you can bet on it.