Regarding portabiltiy: My 220 unit (Hobart 187) is pretty portable and will run on a 14 gauge 60 foot extension cord. I can pick it up with one arm but it is pretty heavy.
If you want to do real frame work, I wouldn't recommend a 110v unit. If it is welding on mounting tabs for something that won't kill you if it falls off, then a 110 is OK...