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.
So many good ones. Some already mentioned, but ones that weren’t: Shield hero has two bangers. Fate stay has a few. Re: Creators. Dimension W. Gate’s opening is really good and captures the feel of the show so well…Does Castlevania count? Cause that new bloody tears version is fire.