Fish’s strength is in having good defaults that makes it work well out of the box. Fish’s downside is not being POSIX compatible [1] though its creators would argue they deliberately avoided POSIX weaknesses.
If you already have Zsh configured well then Fish probably wouldn’t offer a huge advantage.
If you already have Zsh configured well then Fish probably wouldn’t offer a huge advantage.
[1]: https://en.wikipedia.org/wiki/Fish_(Unix_shell)#Bash/fish_tr...