When it comes to over-the-counter acne medications, there is one clear winner: benzoyl peroxide. When it is applied properly it can reliably and completely clear the skin. The only other FDA-approved over-the-counter treatments are salicylic acid, sulfur, and resorcinol, all of which come with drawbacks, not the least of which being that none of them completely clear the skin.
A helper: alpha-hydroxy-acids: Alpha hydroxy acids, like glycolic acid, are not officially FDA-approved acne medications. However, glycolic acid is available over-the-counter in up to 10% strength, and can powerfully exfoliate the skin, increasing the power of benzoyl peroxide.