$() for me, to quote from
https://www.shellcheck.net/wiki/SC2006
Backtick command substitution
`...`is legacy syntax with several issues.
- It has a series of undefined behaviors related to quoting in POSIX.
- It imposes a custom escaping mode with surprising results.
- It's exceptionally hard to nest.
$(...)command substitution has none of these problems, and is therefore strongly encouraged.
That's good. There are also editors that can run it for you and highlight the issues whilst you type, neovim being one.