The best replacement for ksh is bash.

The best alternatives to ksh are rated as following:
★★★★★  bash
★★★  sh
★★★  csh
★★  ksh93
★★  zsh
  bash scripting
  tsh
  pdksh
  naira
  sh unix

Your alternative for ksh is not listed? Suggest!
Speaking about ksh, one probably shouldn't forget about tab completion.

Other search terms related to ksh and their ratings are:
★★★★★ tab completion
You have in mind a companion for ksh and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of ksh in all years. Click on graph for more.
ksh
bash
sh