Hi - we've implemented the Confluence wiki for internal communication, although not for the purpose that you've listed. It can be buggy, although it's easy to set up and use.

We implemented media wiki but are using it more as a technical support tool. As mentioned earlier, it can be very difficult to get people to contribute to Wiki pages. There is also a bit of a learning curve when it comes to formatting wiki pages.

We have tried using SharePoint Wiki to boost info sharing. The effect is below my expectation. The reason is that it not mature to apply different requirements.
However, if you can develop some features by yourself, maybe SharePoint Wiki is also a good feature to harness.
Here is a tool which is useful if you use SP wiki.It is called SharePoint Wiki Redirect SharePoint Wiki Redirect.
Cheers