Which Mig welder to buy?

Stop by your local welding supply house (you'll be buying gas, wire, and such from them anyhow) and see what they have on the floor in the way of trade-ins or reconditioned (warranty repair) units. Keep in mind that with the lower priced 140 amp models you are usually just getting the transformer and by the time you get a gas regulator you're not too far from the price of a 160 amp which is about all you can typically run 110. The really cheap units don't have an internal gas valve any you're stuck with flux core wire.

FWIW I have a Hobart 187 that I bought from Northern Tool. Got a pretty fair price, but my local shop would have met their price. They still made me a deal on a package of new gloves, wire, gas bottle, spatter gel, a cool auto-dark shield and basic hand tools.

Check you local shop before you pull the trigger online...