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.
Someone already said Cowboy Bebop, so I’ll say Kids on the Slope.
It’s another series directed by Shinichiro Watanabe with Yoko Kanno doing a lot of the composition.
Yoko Kanno doing remixes of classic jazz songs is double cheating. 🤣️
I also agree that it’s very good!