I bought a used Lincoln 250 amp wire feed, and I think it is one of the best purchases I have ever made. I would be just as happy with a Miller, it's just that the Lincoln was available. I have a Miller Dimension 400 stick welder as well, ( don't worry, I found it at the auction for $700.00, the auctioneer cried when he dropped the hammer ). I used to have a 110V wire feed with the 4 position switch to select the heat, and it worked fine. The difference is that the big welder with its infinite voltage and amperage controls makes welding sheet metal so easy that I sometimes think I know what I'm doing. My thought is to buy the best machine you can afford. I have MIG, TIG, stick, and gas units, and I use the MIG about 80% of the time.
Bob