If you mean converting shell script between the two, this is not difficult. However, I can't recall anyone ever having free time to do such a thing. Once a shell script is written, it serves it purpose. Converting it to another scripting language (i.e KSH, SH, etc) it not something UNIX admins normally do.
Converting old SH and KSH scripts to PERL or PHP is a often worthwhile; but then again, there should be a compelling reason. If it is a homework problem, that is a different story. In class, we do a lot of seemingly meaningless exercises to learn by practice. This is not a homework board, BTW.
If you are asking about the differences learning the different shells on the command line, that depends on the features you prefer in a shell environment. I only use KSH, others use and love other shells. However, just because one loves KSH does not mean they spend time translating SH scripts to KSH.