The opposite of "un-handiest" is "handiest." This word denotes convenience and ease in using something. When something is "handy," it is within easy reach and readily available. It is something that can be used without much difficulty or delay. For example, a tool that is "handy" can be easily accessed and used to complete a task efficiently. Similarly, a phone that is "handy" is easily accessible and can be used to contact someone quickly. Thus, the antonyms of "un-handiest" suggest a state of usefulness, convenience, and accessibility.