I have an older Lincoln SP125 plus, and I've used other 120 V machines as well. This (older) Lincoln is a good machine within the limits of the lower input voltage. I sold a 220V Miller 160 SP and bought the smaller welder as I still wanted a decent welder for small jobs after I stopped building race cars and such. I simply could not justify the space needed in my small shop.
I bought the Lincoln over the then current Miller, Hobart and other 120V offerings because at the time, a lot of them had aluminum wound transformers.
I think all of the major welder makers do a good job, but get the cover off, and/or get to the specs and see what they did inside. The small boxes are limited enough without further limiting them with Aluminum. (No Clue how the current offerings are built)
With the small 120 V machines you have a choice (usually) of flux core, or non flux core and using a shielding gas. Argon, CO2, or a mix. Using a shielding gas take more power for the same weld, but you do get a cleaner weld with less spatter. Flux core will leave some spatter, not anything like Arc however.
If you want to weld aluminum, you will need a shielding gas as, as far as I know, they do not make a flux core for aluminum. You will also need other things as well.
Agreed on taking a welding class at a community college. Welding is not something I recommend leaning by trial and error, nor from Joe average welder. In a class environment you get the background (and the developed training materials) that even if the welder knows his stuff, he may not have the ability to truly teach you at that level.