About Ubuntu: bash is the default interactive shell. dash was chosen as the default system shell (/bin/sh) mainly because it is significantly faster than bash and so Ubuntu starts up signifcantly faster.
https://wiki.ubuntu.com/DashAsBinSh
Also, the memory requirements really are a lot lower than Windows:
Ubuntu vs. Windows memory, and a backup solution | Developer World - InfoWorld
The OP likes to write scripts that should run on multiples platforms, so than it is good to have POSIX-only compliant dash around for testing, since scripts that work in dash, will likely work in other POSIX compliant shells too..
So I'd say Ubuntu may be a good choice.