Since you already stick weld, there will be a zero learning curve for MIG once you get used to setting up the machine. If you paln to weld in the 1/4 inch range, I'd reccommend at least a 180-amp class machine.
Hobart, Miller and Lincoln make great samll MIG units.
I own a Millermatic 135, but I plan to upgrade to the MM210 this year. The 135 is a great macine, but it just can't make critical welds on something like a trailer.
Hang on to the stick rig - you'll need it.
Be well.
hank