Ok, lets get a little technical here. 110 AC has a single wave that goes back and forth. The MIG has a transformer that converts it to DC. 220 AC has two waves that are transformed into DC. Being the two waves intersect as they go back and forth they have this average that is more constant. Thus, the 220 welder is a more controled welder. It will not be as effected by dirty metal and will provide a better weld. If you really want an awsome welder, go three phase, then you have three waves that have a much more constant intersect. You can weld through just about anything. I got spoiled at the last shop I worked at. We had an Arco Three phase 240 that was incredable.
Now, that being said, I use a Millermatic 135 at work nearly every day and it really does do a nice job for us (we have three of them). DO NOT EVEN THINK of using flux core. The money for the gas is CHEAP vs how much better it works.
