I like ksh actually. It's a bit more consistent than bash because it does not try to support any csh constructs. tcsh, in my experience, is least compatible with other shells, and I avoid it. I try to write scripts to sh, but ksh does have some nice features like exporting and setting a variable on one line. I try to preserve compatibility with bash as well, since it is full-featured and common. To write portable shell scripts, which is more important than selecting the "best" shell, you might consult this book.
Portable Shell Programming: An Extensive Collection of Bourne Shell Examples (HP Professional Series) by Bruce Blinn (Paperback - Oct 29, 1995)
amazon.com
