With dialogue, I generally aim for a slightly optimized version of how people would actually talk. That is, I consider many ways a character could express an idea in that given moment and choose the one that works best. Not only am I looking at the “meat” of the line — the reason why they’re saying it — but also how the line ends. Ideally, each line of dialogue invites the next line, either through an implied question or challenge (“You wouldn’t say he’s arrogant, though.”), or patterns that suggest what’s to follow.
The danger is that being too clever can make something feel written — the audience becomes aware of the writer, rather than the character. You have to consider the genre and the audience. One of the most sobering jobs in a rewrite is killing dialogue that is terrific but wrong.