Which adjective best describes someone who is enthusiastic and lively?

The adjective that best describes someone who is enthusiastic and lively is "exuberant." This term conveys a sense of energetic enthusiasm and excitement. An exuberant person often displays a joyful and spirited demeanor, showing a zest for life that is both infectious and uplifting. It captures not only enthusiasm but also a lively and spirited character, making it a perfect fit for someone who embodies those traits.

While "zestful" also relates to enthusiasm and vigor, it typically emphasizes a keen enjoyment of life rather than the uncontained energy that "exuberant" suggests. The other terms, "pensive" and "ponderous," evoke feelings of deep thoughtfulness or heaviness, respectively, which are contrary to the concept of being lively and enthusiastic. Thus, "exuberant" stands out as the most appropriate choice for someone that embodies enthusiasm and liveliness.