You can't go wrong with a Miller, Linclon, or even a Hobart welder. Having a 220 powered unit would be a real plus. With a 110 unit you have restrictions to the metal thickness that the average hobby welder might need. We are probably talking MIG welding here as opposed to stick, and TIG. As Mig is much easier to work with and learn. If you go with MIG, plan on getting a bottle of mix gas to go with it. Flux core wire is not as clean, and straight gas is not quite as good as mix gas.
So the perfect welder for a car builder in my opinon, is a 220, name brand, wire feed, welder with mix gas. You may also want a good auto hood, as that helps the beginner welder learn much faster.