The word "crumbiest" means the most full of crumbs or the lowest quality. Some antonyms for "crumbiest" might include words such as cleanest, neatest, finest, or highest quality. In terms of cleanliness, antonyms for "crumbiest" might include tidy, immaculate, or spotless. In terms of quality, antonyms might include luxurious, elegant, sophisticated, or top-notch. The context in which "crumbiest" is used will determine the most appropriate antonym. Overall, however, the opposite of "crumbiest" is generally something that is clean and of high quality rather than dirty and of low quality.