Note, while you should feel free to use any interactive shell you like, you should only write scripts with POSIX sh. A friend of mine is working on another shell, mrsh, which aims to be POSIX-sh-as-a-library and will serve as the basis for building more sophisticated interactive shells on a POSIX base, if anyone is interested in that: https://git.sr.ht/~emersion/mrsh
While that's true for portability (there's obviously reasons why nearly all distros ship with a POSIX sh compatible shell at /bin/sh), for simple tasks on my own system, oftentimes I simply want to get the job done without banging my head against a wall dealing with all the idiosyncrasies of sh. For internal use, I think this project excels for automation and administration tasks. Of course, I probably wouldn't ship…
POSIX shell is not really worse than bash or any of the other choices imo. For tasks to which it's not suited, bash et al probably isn't either, and you should just use Python.