I would find it hard to pick out a best anime ending, well I nominate the 2006 version of Kanon, it was not the hapiest ending in the world, but I love it. Clannad After Story aswell, kind of the idea that a lot really hapends, and the ending felt so deserved for the characters.
@ Yonako-Kitti
I see that you are a fan of the Haruhi series, well the ending song Hare Hare Yukai is indeed good, I keep all the different character versions in my playlist. But I am also a fan of the original broadcasting order ending episode of the first series, which is actually placed about halfway, second season's was also indeed good, and everything about the movie was brilliant.
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Through dream I travel, at lantern's call
To consume the flames of a kingdom's fall