312 wire but you will struggle getting it on small reels. If it's not structural go with standard s/steel wire.
weldequip
"sigma face formation"
309L in wire or electrode, this would be a better choice because you can stress relieve 309, 312 you cant cant stress relieve, also if you use 312 on multipass runs you can get embrittlement of the weld caused by sigma face formation.