In your experience, what's the best wiki engine for small business intranet documentation?

We use DokuWiki, which is an open source, well maintained wiki software. It's pretty easy to use, although it's not as intuitive as it could be. See https://www.dokuwiki.org/dokuwiki for more information. I haven't compared it to others, so I can't say it's the "best", but it works well for us.