I have a Miller 135 and I absolutely love it. It depends on what you're going to do with it. A lot of people tell you that you should step up to bigger machines to do frame work but Kyle Tucker at DS&E personally told me that he uses a Miller 135 on a lot of his projects (and no I'm not making that up). I'm using mine for sheetmetal and subframe stuff. It'll handle thicker wire and metal if need be, but not in a commercial situation. If your going to Mig welding thick metal for many years to come than it is advised you step up to the 220 machines as they can handle a heavier work load. But the regular amp machines will do just fine for many applications.
The greatest tool I've ever purchased. It just doesn't get any better than having a welder out in the garage.
You're speaking as if there is a grey area concerning machine choice. There isn't. If you know you'll be welding 1/4 to 1/4 mild steel plate only once in your life, and you absolutely must do it with your own machine, then a 135 will NOT produce a structurally sound weld, period.
Yes, 135's are fine for stock frame work, if you don't mind a 20% duty cycle.
-Matt
Welders: The only people that think a co-worker catching on fire is funny.