I prefer ksh93. I do not mind bash for interactive use and I suspect that many users use it mostly in that fashion. However for scripting work I try to use ksh93 whenever possible. It knows features like e.g. advanced job control, associative arrays, a.b. variables, call by value and call by name in functions, the way it handles locality in loops and floating point arithmetic. Plus (big plus) in my experience ksh93 really is a lot faster then any other shell I know.

I prefer ksh. I'm a huge fan of using automation to enforce standards. The ability of ksh to use FPATH and autoload to define ksh functions is incredible. This allows us to write common functions once that can be reused by everyone, eliminating the need to re-invent the wheel each time. This can be done in other shells, just not as cleanly as the ksh, IMO.