As far as I can tell, XZ is a container that uses the LZMA2 algorithm (i.e. extended LZMA); but e.g.
$ xz foo/
complains about foo/ being a directory. So presumably the correct way to preserve directories with XZ is with tar; then what is the difference between tar --lzma and tar --xz?
(Note that I do explicitly want ownership and permissions preserved, which is why I'm not just using 7z.)
This options control which external binary tar calls for compressing its data stream: lzma and xz respectively. While both of them uses the same compression algorithm by default, xz is considered more up-to-date and feature rich, with lzma being somewhat legacy tool. Modern version of xz-utils provides both commands, with lzma being an 'alias' for xz --format=lzma (man xz).
xz-utils, there's effectively no difference?
tar. xz archives can be concatenated, while lzma cannot (limitations of container format) — that's the only notable difference for me, applying xz was used with lzma compression.