I have a hobart 125 or 135...can't remember...what i liked about it was I didn't have the money to throw for the gas regulator stuff to begin with and they sold it seperately so it helped my budget.
A buddy of mine who is a professional weldor also owns a 125 or 135, he said it's a great unit. I'm a computer guy by trade but I would say to go with a hobart, lincoln or miller, although I believe that hobart and miller are the same company now.
the 125/135 and I'd imagine the 140 aren't going to be capable of handling really thick metal, so make sure whatever you get that it can handle whatever you are planning on welding. Next, the flux core wire is ok for crap jobs but it's not optimal for even learning really good because it's messy. If you can afford it, go for the solid core with shielding gas kit...don't forget gloves and hood as well.
I'm not sure if it still exists but hobart had a pretty good official forum.