A couple of things that have not been mentioned above that I considered when purchasing my first welder.
1. The cost of the welder is only part of the equation. You also need a hood, gloves, leathers, magnets, gas, tank, cart, etc.
2. My input is to purchase the VERY best hood you can afford, your eye's are worth it, and welding is MUCH easier to learn with a good hood.
3. Buy the best welder you can afford.
4. Miller, Lincoln and Hobart are all reasonable products, I prefer Miller, and I suspect that most people agree that as a general rule the Miller products are better than the others.
5. Size can be important depending on where you are useing it. Most standard garages can not handle a full size unit, they just take up too much space. The smaller units on a cart with tanks is much easier to store out of the way.
6. 220V is much more capable than a 110 unit for thicker materials, you can consider multiple passes on some applications but I wouldn't want to plan on a smaller unit and doing multiple passes for much of what you want to do with it.
7. I would only consider a 110 portable unit as a second unit for my purposes, just isn't useful to me. I have two friends who got 110 units do to that idea and neither of them have ever traveled with it in the years that they have both had them.
8. I have a Miller 220V 175 unit and I love it. I have access to a 250 unit with an additional AL spool gun also and it is awsome. The reason I got the 175 is due to space, it is much more practicle in my work space.
Michael