My shop is equipped with a MIG welder, a TIG welder, and a plasma cutter. For someone building their first shop, here's how I think about which tool to buy first.

MIG first, without question. The MIG welder handles 80% of restoration welding — panel patches, floor replacements, chassis repairs, bracket fabrication. The learning curve is achievable. The results on sheet metal are excellent when you set the machine correctly and maintain proper technique.

Plasma cutter second. It changes panel removal from a grinding operation to a precision cut. TIG last, because TIG requires significant skill to use effectively and the scenarios where TIG is meaningfully better than MIG on a typical restoration are limited. Get the TIG after you've mastered the MIG.