As of this moment, I'd have to say the easy winner is Grand Escape from the new movie Weathering With You. I simply can't get tired of listening to that song or watching the official MV.
Also, for special reasons, the somewhat-recent Honey Works song
Erande Kurete Arigatou. Not so much because I like the song itself as because it gives a conclusion to a romance that'd been left frustratingly in the air for a long time:
Spoiler:
The Moment You Fall in Love is a rather sweet and entertaining romance anime movie that I can still enjoy from time to time, though it ended without really saying whether Kotaro and Hina would ever end up together. This new song delves into their future, the way they continued to bicker and miss opportunities until they'd grown up, but still cared for one another, how Kotaro skipped out early from work to surprise Hina on her 20th birthday, and how eventually Hina decided that she was too embarrassed to directly say anything to him about what she wanted, so she just started telling her friends that he was her boyfriend, all around a chorus of the two thinking how they'd love to go back and tell their past selves that it's OK, it'll work out, that he's going to make her happy, that she's truly happy, etc. For a guy who really liked the story and was frustrated to not know how their story would end, this was a great song.
Only thing is that the full song can't be found on YouTube, only Nico.