Unwieldiest means difficult to handle, manage, or use because of its size, shape, or complexity. As an antonym, we can use the word "manageable" which means easy to handle, direct, or control. Another antonym could be "nimble" which means agile, quick, or light in movement. If we want to convey the idea of something being easy to manage and maneuver, we could use the word "flexible". The word "compact" could also be an antonym for unwieldiest, as it means something small and efficient that is easy to handle and transport. To sum up, these antonyms provide alternative options in language for describing objects, such as products or machines, that are easy to control or manage.