of those 3, i'd personally go with the used millermatic 135
check craigslist or whatever else as well, if from the pawn shop, make sure you get the gas regulator with it, just because. make sure it comes with wire rollers and the little stuff and such.
personally I have an older model hobart handle 140 and it does all the things it needs to. the current model has 5 different volt settings for more adjustment, i swapped over my earth clamp to a magnet. retail is about $500 new
if going with new, the millermatic 141 is a nice unit, but retails closer to $800. it has 10 different settings for voltage for more control. Not that it really matters to the 'everyman'
lincoln weld pak 140 looks to be the same options as the hobart 140 and about the same price. coin toss between the two.
https://www.millerwelds.com/files/ow...O1324D_MIL.pdf
millermatic 135 owners manual