Which term would best describe someone who is clever or amusing in conversation?

The term "witty" is the most fitting choice for describing someone who is clever or amusing in conversation. Witty individuals possess an ability to express themselves in a clever and humorous manner, often using wordplay, puns, or quick rejoinders that engage others and elicit laughter. This quality enhances communication, making conversations lively and entertaining.

While "vivid" pertains to being bright, intense, or full of life, and could apply to descriptions of imagery or emotions, it does not specifically encapsulate the cleverness or humor aspect in conversation. "Sullen" characterizes someone who is gloomy or sulky, which is in stark contrast to clever or amusing dialogue. "Urbane" refers to someone who is sophisticated and polished in manners but does not inherently imply humor or cleverness in conversation. Thus, "witty" is the term that best captures the essence of being clever and amusing in dialogue.