After reviewing as many Wiki offerings as I could I have chosen Deki Wiki.
My community of users would be unwilling to learn to use the editors of the other systems I examined. There may be extensions to fix this but I want to write content not code.
Deki Wiki enables User Generated Content via a wyswhg editor very similar to MS Word. No proprietary markup language.
I host my site on Go Daddy. They install mediawiki and pmwiki as part of their hosting offering. So I tried out mediawiki. The lack of documentation and the (how can I be polite about this?) rat's nest of the projects site was so confusing and impenetrable to me as a novice that I went shopping for a better solution. I believe I have found it in Deki Wiki.
I wanted to use it as a seamless extension of my site but opted to use MindTouch's free hosting and provide links back and forth on my site and my Wiki.
The cons so far are:
1. Go Daddy will not allow sufficient control of shared hosting servers to install the program. they would require me to have a virtual private server at the least.
2. The user community forum at forums.opengarden.org is still relatively small. I am used to the huge community of Joomla users and the support available via their forums.
3. No books -- Deki Beginners etc are not yet available. There are a few available (though with poor Amazon reviews) for mediawiki.
4. I do not know how deep the developer community is on this project. It looks to me, after a cursory examination that it is just MindTouch so far.