Which Mig welder to buy?

Dad taught me to weld with a Lincoln sp-100 setup with the argon/co mix. That was 21 years ago and it still welds great and often. It has not been babied, and has seen a lot of hours. Anything over 3/16 I'll preheat for
Max penetration. I would say even with preheating and champhering, 5/16 is the limit for that little machine.