Linux

I use a mix of fish and nu depending on what I'm doing. NuShell is great but still pretty buggy, so I use fish as my default and switch to it when I want to use its features.

I still write most of my stuff in bash however since servers I work with typically only have bash, and so are potential coworkers.

But locally I see no point restricting myself to a POSIX compatible shell, especially for interactive shells. The easier and faster it is to use and customize the better. Being able to parse and use JSON and CSV and other things easily and natively right in the shell is a major quality of life improvement!

If you want you can install starship, which provides a lot of the nifty prompt customization I see in other people's zsh configs. I've been using it with bash for a few months now and like it a lot.

Let the religious shell wars begin ... again

Only right answer is of course TCSH. Not much documentation and support, ancient but still receives new bugs in 2021 (on Debian), but attackers hate it! (I love it)

My real suggestion is to learn zsh and fish (and bash). Try using them for all your purposes and in the end you will automatically find the one (or more of them) that suits you best and that you like most for your daily tasks.