Hmmmm... Well, I like wikipedia's software, but lets not rule out others. I'd prefer one of the following:
ModWiki - I use this for my personal wiki, and really like it. I don't like the way it handles uploads though! It works for me, but for a large public one we might run into issues.
Twiki - Has a cult following...
As max mentioned earlier, WikiPedia's software is nice, but I don't know much about it...
UPDATE:
After looking into Wikipedia's features list, I have mixed feelings. I'm not sure the complexity is warranted in this situation...