I think it depends on the condition of the paint at the moment. It could need a clay, compound, glaze, polish, sealant, etc....
If you are looking for something in a single step process I would recommend a cleaner/wax because it has a small amount of abrasion to remove defects. I like the McGuires professional line of waxes and cleaner/waxes.
If you do a lot of highway driving I would recommend a sealant over a wax because it creates a harder shell than waxes.
Another question to ask yourself is, how much money do you want to spend on it? You can get some good waxes for as little as $10 and up to $100.