ArtMetal

For the work you say you're most likely to be doing, the MIG is a very good choice. Yes, TIG is cleaner, more versatile at different metals and more capable of producing high-quality welds, but it is not a quick method, either form the standpoint of the learning curve or production speed.

With MIG, you just pick up the glue gun and get right to it. Unless you start regularly working with stock heavier than 3/8", the duty cycle shouldn't be an issue. You'll be spending time grinding, fitting, cleaning and so on, while the machine cools. A MIG gun won't get too hot to hold, either. Unless you get a water-cooled TIG torch, you'll find that extended welding times leave you with a torch that you can't hold comfortably.

You can use the MIG for steel, stainless and silicon bronze with no changes other than maybe gas, and it works fine for out-of-position welding. For aluminum you may need a spool gun, or you may be able to get away with just a Teflon feeder liner, depending on the size and alloy of the aluminum. If you need to weld pretty heavy steel stock, you can do multiple passes and/or use dual-shield wire. The dual-shield gives really pretty welds with very little spatter, but it ain't cheap.

I have O/A, stick, MIG and TIG welders in my shop and the MIG gets the most use by far. For building jigs, fixtures, sculptures and repairs, it is the ticket. For the fussy stuff, the tiny stuff, and the exotic metals, TIG is the way to go. TIG is no fun at all when used out-of-position, though. For on-site instalation/repair work where spatter and smoke would be an issue, TIG simply cannot be beat. You can work right next to milady's damask draperies without fear, something you can't do with any other type of welding. Little or no clean-up, either. Each method has its place.

I'll note here that for working with steel and some stainless, you can do a lot with an O/A torch. The skills required for good O/A welding are much the same as for good TIG welding, and the results can be similar, particularly on mild steel. You would likely want the O/A torch for heating and cutting, as well.

In short, I'd advise sticking with the MIG unit. You'll be happy with it and you can get a TIG unit later if/when you have a real *need* for it.