Not for sure on the best. Flux core wire is good to use in outside conditions but usually leaves a lot of splatter. You will want to use thin wire like .023 and make sure the welder is adjusted properly for the thickness of your metal or you will be burning holes through it really fast. If your welder is capable of using the argon gas setup with regular steel mig wire it makes for a lot cleaner weld. But argon gas is usually better for indoor use as the wind will blow the gas out before you can use it.