I'm curious as to what size (GMAW) mig machine and the size wire you will be using. I ask that to say this, if you have a low amp/small GMAW machine, you may be better off going the low-hy stick(SMAW) route. Also note that GMAW is fussier about cleanliness of the materials at the joint than SMAW or FCAW. Fluxcore (FCAW) is more forgiving about the cleanliness and is deeper digging for more penetration than the solid wire of mig(GMAW). And FCAW offers a wire that is gasless(no external shielding gas needed), where as the GMAW wire does not. FCAW and SMAW can be run out of position is an other advantage over GMAW.
Just a few thoughts to ponder,
John Wright
Give a little more info about your situation, I'm sure other forum users will have more to add.