I personally don't give a fuck about the declined performance of updates because I have a good pc and there's plenty of very accessible mods to use to solve most of it (& I've never hosted servers for more than 5 people, which didn't really make a severe impact either)… So I'm just gonna vote based on the content and what I personally have positive memories of.
Beta 1.4: Far from perfect but this was where I started, I still have a lot of nostalgia for this paticular version, even if it didn't really last long. At this point all of the beta versions before 1.8 just feels like a completely different game, but it's still familiar enough to enjoy all the same.
1.5: I first started trying mods during this version, whether it was a load of laggy packs at the time or more standalone things. I mainly just hold this version so high because of a shapeshifterZ mod I used to play with and a server a developer hosted to play with others who used it. I met many good people there and I still kind of regret never having skype or any way of staying in touch after the server abruptly closed for good, as I only ever saw one person from there briefly again, a few months after that
1.17-1.18: I couldn't give any less of a fuck about the performance impact, I love the new caves and world generation and it was way the fuck overdue, same for 1.13's oceans. It's way easier and more common to find cool as fuck places to make bases now rather than always sticking to shattered fucking savannahs for mountains or a shitty hill of the actual "extreme" hills.
1.9: Elytras. That's it, that's what I loved. The combat was also not really something I minded, I prefer the current version for when I don't want to obliterate my hands for hours holding sprint and spam clicking just to "combo". Plus I mainly play pve anyway, so makes little difference to me. (Yeah I prefer 1.8 for pvp although won't ignore how fucking stupid it feels sometimes, both systems have flaws and I doubt the upcoming one will solve any of them enough to make people happy. Fuck that shitty bow change, revert that shit asses who gives a fuck about realism)
1.7 since I believe that was when amplified worlds were introduced? Until 1.17-1.18 world gen this solved most of my issues with old world gen and shit will never not look phenomenonal with shaders