I have already decided on having at least a 210 class machine for my next mig. I will also go with a spool gun for aluminum or gas shielded cored wires. I want to go with a tig eventually as well, but for practicality I'm better off in the current long term with a better mig and spool gun set up. For thin stock, my current welder, once converted to mig, will be perfect for sheet metal(HH 125).I bought a little mig machine a few years ago, just piddled with it. I had welded in school (stick), but this was my first mig. I quickly realized I needed a bigger machine. So I saved some pennies and upgraded to a bigger mig machine.
I had several projects I wanted to do out of aluminum and also wanted better results on thin steel. I saved my pennies, a ton of them, and bought myself a tig.
I never had anyone show me how to weld with tig or mig, I had stick welded before I had welding in school. Pretty much just learned it on my own. Once you have the idea down its all about technique from there.
I tig almost everything now, just like doing it more than mig.