Available in most UNIX system, ksh is standard-comliant, clearly designed, well-rounded.
I think books,helps in ksh is enough and clear, especially the O'Reilly book.
Bash is a mass. I keep it as root login shell for Linux at home only.
For interactive use, I prefer zsh on Linux/UNIX. I run scripts in zsh, but I'll test most of my scripts, functions in AIX ksh though.
