as stated above, stick with the the big three: Lincoln, Miller or Hobart... and inert gas. forget about flux core for anything on light gauge metal...
I've got a few welders in my shop...
an 8 year old Astro Mig, which i love... one of the Italian made models, 130amp, 110v or 220v, runs clean and smooth, takes tons of abuse... but REALLY TOUGH to find parts for! great little welder, but i'd not recommend it to anyone because of difficulty getting replacement parts and consumables. can't find the Italian made ones anymore, either... and the Asian made ones are complete crud.
a Hobart Handler 180... great little machine, easy to get parts/consumables for. this used to be my primary body work/sheetmetal welder.
a ~30 year old Miller 220v mig: parts/comsumables are readily available online or nearly any local welding supply.
a very old ac/dc arc welder... 220V, 200A, can probably put another 50 years of use on it and still never need to replace a part. also have an old (50's era, i think) Homart scratch-start TIG setup for it, that parts are nearly impossible to locate.
most welding i do for anything, sheetmetal included, is oxy acetylene...
i've got an old Smith mini aircraft-style and a ~40 year old Harris 19-2 with modified valves. can weld damn near anything with oxy/ace, including aluminum with astounding results. surely takes a lot more practice, but something about it just feels "right" to me.