Nobody mentioned the Debian based standard for sh, Its the Debian Almquist shell dash. Its is fully POSIX compliant and has a very fast startup, which is why Debian/Ubuntu use it for /bin/sh.
So I use bash for my interactive shell, but only dash for scripting. That way i know my scripts are at least POSIX compliant, and will run on any other POSIX shell. ... I know portability is more than the shell, but its where I draw the line.
