I own a welding supply business. 140A is OK for sheetmetal, anything much bigger will not penetrate and you will get something that looks like a weld but is not.
180A is a nice size. We sell both Lincoln and Miller, they are both fine. A new option is Forney. The Forney uses standard Tweco consumables and has the heavy duty wire drive like the industrial grade Lincoln machines.
I personally would not buy a Harbor Freight. If it needs repair you are SOL.
I guess there is a big difference between owning a business and being familiar with the product.
I have welded 3/8 plate with my little 110 machine then beat the crap out of the piece. I ended up tearing the plate but never broke the weld.
It was good enough for me to put together a goose neck trailer hitch plate for the bed of my truck. That hauled 18,000 lbs of steel from OKC to DFW.
Tell me again how bad a 110 VAC machine is.
I no doubt maxed my machine but with careful prep and proper use you can do quite a bit of work with them.
