TBH the penetration on both MIG and MMA is the same up to about 5mm (with the right kit). IMO of course. And certainly, for the majority of the chassis and plates (1.6mm and 3mm) I very much doubt there would be much to choose between them. I do stand to be corrected though.
It is easy to have a MIG weld that looks nice, but has no pen.
MIG is easier for people to learn.
Stick can be a bit 'fierce' for thinner stuff, although, it is possible in the right hands, with a decent MMA kit.
A cheap MMA kit can be had for a lot less than a MIG.
No gas rental with MMA
Horses for courses, but, on thin stuff like we use for 95% of the chassis and plates, MIG would be my first choice everytime.
I never really got on with stick in the past, and treated myself to a nice MIG, so that is what I use.
I am looking at a nice MMA set (possibly a Lorch
), but TBH I don't really have a use for one, so it would just gather dust.
Both processes have their place, as does TIG (I want one of those too, but it's only to do the tank
) but I have almost always regarded MMA as a more 'industrial' process, structural steelwork, beefy gates, outdoor work.
Although, on a visit to a steel fabricators for work, they were MIG'ing everything upto about 20mm thick, just doing multipass.
I asked why, their answer;
Faster and cheaper