Your not comparing apples to apples. The miller 211 is closer to the 180C. C is continuios and not a tap machine. And the C is about 300$ U.S. more. All machines have there best and worst. When buying you need to look at what you will be welding today and tomorrow. Buying something a little bigger is a good thing, but you have to be budget minded also. The plus to the licoln machine is there rebates right now.
I use miller's at work, But I prefer a lincoln at home. The best you can do is find someone with one and see if they will let you weld with it and see if it is what you like. If it feels good in your hands before you buy. There is less regret later.
I agree, they are very different machines. That's my point, actually. For about $350 more you get 110/220 versatility, the Autoset feature, and 30 amps more welding capacity.
There are a few more differences in the 180 Mig Pak and the 180C besides the tap vs. continuous voltage adjust. I think the drive mechanism in the Mig Pak is plastic vs. cast aluminum in the heavier duty model, and the transformer windings MAY be different (aluminum vs. copper). Research will tell you what the changes actually are.
After checking, the Lincoln IS spool gun compatible according to what I've read. I'm not saying it isn't a good MIG welder, I'm just saying it's worth exploring a bit further.
If it were me, and my budget wouldn't allow the Miller 211, I'd buy the Lincoln on sale this week for $619 and sit on it while I did some more research on pricing and upgrades. If I couldn't do any better I'd open the box and happily start welding.
My experience with Canadian Tire and Princess Auto, etc. has been that while the price looks good up front, you can often do better at a welding supply store, such as Air Liquide, Praxair, etc. Both of those sell Lincoln and Miller side by each which makes it easy to compare, plus you have a sales staff that should know them both inside out.
Just walking in the door and asking the price usually doesn't do it, though. I try to haggle the price down as far as I can, then make my decision. There's often at least $100 fat on the first price.
When I bought my 135 Miller, the deal included an owned tank of C25 Autoweld gas, more wire, and a helmet. By getting all three at the same time I got a further discount over the individual prices.
Another benefit is you'd be buying from a servicing dealer, not a box store. That can be a Very Good Thing in the unlikely event you do have problems.
Sean