There are several antonyms for the phrase "most nonfunctional", including "most functional", "efficient", "effective", and "useful". These words imply a level of optimization and productivity that is lacking in something that is nonfunctional. In contrast to nonfunctional, functional objects are capable of fulfilling their intended purpose or task. Efficiency suggests that something is completed with minimal waste of time or resources. On the other hand, something that is effective produces the desired outcome or result. Lastly, useful denotes that an object has a practical or beneficial value. Ultimately, these antonyms represent the opposite qualities of the characteristic of most nonfunctional.