My first impression of MediaWiki was that it was too complex for the needs of a medium-sized corporation. I selected MoinMoin because it is also very good and has less infrastructure requirements.
Now in other job I'm using MediaWiki and I found out that it is not too complex after all, that it is very mature and, above all, that its extensibility is very good.
I'd settle for MediaWiki, even for a 1-person wiki... :-)