it depends on what you want to do with it. If all you're going to do is thinner stuff, like fabricating for go karts and such, a cheap 125 amp gasless mig that uses flux core wire would be the easiest for a beginner to learn. The welds aren't as pretty and leave alot of spatter, but you can always grind them down. harbor freight sells some cheap ones. If you get a good one, you could always add a cylinder and regulator later down the road to use regular wire and co2 or argon. My first welder was an arc welder (Lincoln tombstone) and you can do alot with these, but as a beginner it is more difficult as the flux coating hides the weld and makes it tougher to tell what you are doing. Also, it is easier to burn through on thinner metals. You can find used arcwelders for well under $100 pretty regularly. If you are going to do heavier stuff, get a nice 175-250 amp mig, they will run on 220v, but you can weld almost anything from sheetmetal to 3/8" plate. they will set you back $700-$1200 though...as to brands, Hobart, Lincoln, Miller are the better brands, in my opinion.
as to the difference, Arc and mig are both electric resistance welders, Arc welders use a rod coated with flux, and there are many different thicknesses of rod and types of coating for various conditions. rusty metal rod is good for welding dirty old junk together. They come in AC or DC versions, AC welders are cheaper, but DC welds better, especially upside down.
MIG stands for metal inert gas, and replaces the stick with thin wire. Usually, the wire is shielded from oxygen during the weld by a gas (CO2, argon, or a mix of the two), and the wire is fed into the weld by a motor controled with a button on the torch. MIG welders can also use flux cored wire without gas, that is wire with flux inside of it. you have to reverse the polarity on your machine to do this, and the welds arenot as pretty as there is often alot of spatter.
Hope this helps
