[zerogara]

If you care about space more than you care about speed you may want to stick with xz, it is hard to beat or impossible by zstd. So set your own priorities rather than adopt the ones of Arch devs.

As long as there will be support within the tools for xz individual builders of packages for their own use can use either or more.

[SamWhited]

I don't really care about space all that much, but packages I build tend to get uploaded and the people downloading them may not have fast internet. Meanwhile, packages built by my AUR helper I care about speed (seriously, it takes ages to compress then immediately decompress firefox). The problem isn't that I want to optimize for one or the other, it's that AUR helpers generally have a different need than I do when building my packages myself, but for some reason AUR helpers don't override the compression setting for just their install. Probably due to caching like I said which means they can't assume everyone will want compression off all the time, but I'm not sure, that's just a guess.

[ncmncm]

I doubt anybody today has legitimately enough reason to care about space to prefer xz over zstd. The only plausible reason is that some customer, or customer's customer, is only equipped to unpack archaic formats.