5.0
for the rules and character options.
Others, esp Volo's for monster stuff, new magic, items, etc.
I see additional books and rules expansions as purely optional. Mine what you want, ignore the rest.
I don't really find any classes/ options in Tasha's or Xanthar's to be particularly attractive. Same for the races, with the exception of the Aasimar. I felt kinda let down that they included the Tiefling but not it's opposite, the Aasimar in the PHB. Thus, I'm not including any as options in my campaign world. None of us has played it enough to be jaded or sick of the PHB options, yet.
I never saw extras like that as core elements that I HAD to allow- just because it was from an official D&D product. (Because they've NEVER published anything broken, ill thought out, or game breaking in any official publications before, right, lol) Esp, if it's totally wrong for the campaign at hand.
or:
3.0/3.5 I enjoyed playing and DMing it quite a bit. Probably just mine it for ideas and goodies tho, unless I find players who really want to play that edition.
The heavy handed restrictions/ balance decisions of AD&D just don't really fly well, now. too much water under the bridge. The FEEL of the games? HECK yes!! I gotta say, tho- the idea of playing a B/X game, just for old time's sake does have a lot of charm, lol.