Hmm, that's a hard one, I think it was when they rewamped the ocean so you can actually see fishes swimming around. But the introduction to horses was also a good one 1.6 i believe. And now ofcourse we can't forget rewamped nether update also I look forward what they got in store for us inside in that mystical portal in abandoned warden city, maybe another biome which brings new blocks & stuff ^^.
I am all for creativity and more functions and gameplay for the game so every update comes with something useful but since I mostly use now 1.19.2 version of minecraft cause it has stable mods and features I would say that one also ^^.