I write my scripts in zsh, because its extensions are most useful in scripts, and it’s not too hard just to make it available everywhere you need to work (e.g. you can compile it to be installed in ~/zsh and just copy the installation to your home directory on any machine you need to use.

Things like array-linked variables ($path is an array version of $PATH and modifications to one propagate to the other), associative arrays (dictionaries in python) and a handful of other really nice tools (e.g. saner white space handling) make going back to bash for scripts unpleasant.