For me, it’s Gintama. It’s iconic, easily identifiable, and makes sense on a musical level. On the last point, I’m not knowledgeable on the theory, but the Gintama soundtrack, in general, is enjoyable to listen too. If I have to pick one favorite song there, it’s Katsura’s theme.
Yep, Champloo slaps start to finish, I’d say it’s solid tie between it and Bepop.
Also gotta shout out basically any Ghibli OST, especially Howls, so damn good