The antonyms for the phrase "most unspotted" include "tainted," "soiled," "dirty," "blemished," and "stained." These words all suggest that something is not entirely clean or pure, and might have some imperfections or flaws. While "most unspotted" implies that something is completely free of any marks or stains, its antonyms imply the opposite - that something has been marked or stained in some way. It is important to use the right antonym depending on the context of the sentence and the tone of the writing.