I have a MIG welder, but I prefer to use acetylene for thin stuff. If you're repairing a small crack, the MIG gets done so fast the base metal hardly has a chance to warm up. MIG leaves a thick bead that is very difficult to grind down. With gas, I can take my time, get good fusion and end up with a nice flat bead.
I find it humorous that many folks who extol the virtues of TIG over MIG would never consider welding with gas. Yet with steel, the gas and TIG processes are almost identical, the difference being that when you're gas welding you use the inert gases in the flame rather than argon to shield the weld.
For aircraft work, gas and TIG are considered equally acceptable, and MIG is seldom used. The main problem with MIG is the "cold start", where the start of the bead doesn't have good fusion because the base metal is cold.