Hobart and Miller are owned by the same company (ITW) and both are quality machines. Millers are a notch above, but for me as a hobbyist, I am very happy with my Hobart 187, and I have read from some folks that the Handler 220v machines are a notch above comparable Millers.
I have not heard that Tractor Supply branded machines have anything to do with Hobart.
I personally have had serious customer service issues with Lincoln, although your results may be different, that one experience left a bad tast in my mouth about red machines. The case is only one part of the machine. My very expensive high-quality high-zoot built-in-Japan TIG machine has a plastic case.
If you can afford the Miller, it is pretty much the best you can get. I think you can save some $$$ by going with the Hobart if you don't weld every day for 8 hours a day.
All just my opinion, I don't make my living welding.
