I've welded lot's of aluminum with MIG, it works great if everything is set up right. The spool gun is the way to go. You can't weld thin material with the MIG so if it's less than 14 gauge you'll want to TIG it.

[link=http://www.millerwelds.com/education/tech_articles/articles10.php]HERE[/link] is some good info from Miller.