I've tried a few different wiki designs (snipsnap, Xwiki, Wikimedia, Dominowiki) we finally settled on Dominowiki at work - primarily because it doesn't have WYSIWYG editing. Most WYSIWYG editors are simply sources of bugs and frustration. If they work, they take forever to load. I have yet to see one where the wiki markup and the rich text live in perfect harmony.
I would advocate the wikimedia approach where a icon bar ioserts the appropriate wiki markup at the currect cursor location.