I recently switched to CKeditor (with Drupal 6.x), and am very happy with it. The interface loads much quicker and runs more smoothly. It also appears that there's less files cluttering the installation.
The only thing I can't figure out is why the native Firefox spellchecker (the red squiggly lines) is disabled by default. I know that with FCKeditor I could enable it with the following command in my fckeditor.config.js file:
FCKConfig.FirefoxSpellChecker = true ;
What is the equivalent way of doing this in CKeditor?