The right welding process depends on the material, thickness, position, quality needed and production volume. Here's how the common arc processes compare.
MIG (GMAW) — the productivity choice
A continuously-fed wire and shielding gas. Fast, easy to learn, good for steel and aluminium in production and on thicker sections. Less clean than TIG and sensitive to wind (the gas blows away), so it's mostly an indoor process. The default for volume fabrication.
TIG (GTAW) — the quality choice
A non-consumable tungsten electrode with a separate filler rod. The most precise and cleanest process — the go-to for thin material, aluminium, stainless, and anything cosmetic or aerospace. Slow and skill-intensive, so it's for quality over quantity.
Stick (SMAW) — the field choice
A flux-coated consumable electrode; no external gas, so it works outdoors and in the wind. Rugged and portable for structural, repair and site work, tolerant of dirty or rusty steel. Slower, with slag to chip, and not for thin sheet.
Flux-cored, spot and matching to the job
Flux-cored (FCAW) is MIG-speed but self-shielded for outdoor structural work. Resistance spot welding dominates sheet-metal assembly (car bodies). Match the process to the metal and thickness first, then to volume: thin/cosmetic/aluminium → TIG; production steel → MIG; field/structural → stick or FCAW; sheet in volume → spot. Then read the joint with the weld-symbol guide and size it with the weld tool.