If you have 220 power, I would definitely get the more powerful machine. Not having the ability to run higher power is something that you'll probably kick yourself for later. You can always dial it back for thinner materials.
For mobility, I have no clue on that one. I got both of my welders (mig and TIG) with dual voltage, so I can plug it into either 110, or 220. Since I've put 220 in the garage, I've not plugged either of them in to the 110 power. When I bring them elsewhere, I usually have to plug into 110, but it's rare that I bring them elsewhere other than my garage.
If I were in your spot, and you're mostly going to be using it at home, I'd get the 220 machine. If later on you need to be mobile and have to use 110 alot, maybe pick up a cheap 110 machine just for the times you are out?
Daniel Buck - [URL="http://www.danielbuck.net"]www.DanielBuck.net[/URL] - [URL="http://www.dnsfail.com"]www.DNSFAIL.com[/URL]