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.
I’ve found myself listening many times to the whole soundtracks of One-Punch Man and Spy x Family.