Fish is pretty decent and so is oil, but I still use zsh because of its POSIX compatibilty - which, in my opinion is a huge plus.
Pimping zsh with powerlevel10k[1], some custom dotfiles and scripts feels like having enough convenience, while still using POSIX. I use "Pure" theme by the way, because it also works nicely in not so modern Terminals, if you replace PROMPT_CHAR with > instead of using the default unicode one...
If there were only these two to choose from, I can't tell you, which one to use. I would just recommend NOT linking the chosen one to /bin/sh, but using either fish or oil for your daily use cases and linking dash to /bin/sh for keeping your OS scripts POSIX compatible and working.
I, personally, have come to the conclusion, that zsh is good enough for me and will be until something revolutionary happens.
Pimping zsh with powerlevel10k[1], some custom dotfiles and scripts feels like having enough convenience, while still using POSIX. I use "Pure" theme by the way, because it also works nicely in not so modern Terminals, if you replace PROMPT_CHAR with > instead of using the default unicode one...
If there were only these two to choose from, I can't tell you, which one to use. I would just recommend NOT linking the chosen one to /bin/sh, but using either fish or oil for your daily use cases and linking dash to /bin/sh for keeping your OS scripts POSIX compatible and working.
I, personally, have come to the conclusion, that zsh is good enough for me and will be until something revolutionary happens.
[1] https://github.com/romkatv/powerlevel10k