Argon mix is definitely the best for cars in my experience, but nowadays i don't do alot of welding so just get yourself a CO2 fire exinguisher and plug your regulator in, pin the handle close and away you go, it has a little bit more vapour in than the BOC CO2 so the regulator freezes after prolonged use in the winter when welding but if you wait afew minutes for it to warm back up its fine.