The antonyms for "untidier", which means not clean or orderly, would be "neat", "tidy", "organized", "clean", "meticulous", and "spotless". These words imply a sense of orderliness and cleanliness, suggesting that something has been well-maintained and taken care of. When used in the context of a living space, these antonyms suggest a space that is well-kept, arranged in an organized manner, and void of clutter. Additionally, using these words can imply a sense of personal responsibility and attentiveness to detail, which may be qualities that are valued in various contexts, from personal hygiene to workplace productivity.