The antonyms for the word "most unexpressive" are numerous and varied, as it's a relative term that can be interpreted in several ways. Still, some of the most common opposites include emotional, expressive, animated, communicative, demonstrative, effusive, enthusiastic, lively, open, outgoing, responsive, and talkative. Each of these antonyms describes someone who is the opposite of unexpressive, meaning they readily display their emotions, thoughts, and feelings through their words, gestures, or facial expressions. Thus, whichever antonym you choose, it would stand for the polar opposite of "most unexpressive" and depict someone who is vivacious, communicative, and interactive.