We had an expert welder come in to weld our chassis for us. (who just so happened to be my girlfriend's brother) He used a TIG welder (preference? don't know), and the welds look very nice and clean.
He didn't clean any of it, he told me that you only need to clean the oxidation off if you aren't a good welder
It's contrary to what I have read (everywhere), but eh... he's the welder
Something about not heating it too long so you blow a hole in it...
Now to what I personally believe. I have welded only steel with either a MIG or a TIG welder. I am by no means an expert welder, but I can manage to make two peices of metal stick to eachother.
I find the TIG welder easier to manage, it's small and light, but you need a good pair of steady and coordinated hands. I also think TIG is brighter, so it's easier to see what you're doing.
I get neater looking welds with a MIG welder, and you don't need to be as steady or coordinated. It also helps to use two hands on the one thing, so you can keep it a little steadier.
--- im rambling...
I think if you're set up to do aluminum on a MIG welder, go for it. If you've never welded before, get a few hours in on steel before even trying aluminum. MIG is easier to get the hang of, and it will definantly suit your purpose.
Good luck!
Dave