Different Wikis are suitable for different things. TWiki has the best features, but really needs some crafting in terms of appearance. MediaWiki is easily to deploy, is attractive, but is not structured. If you need a structured Wiki with workspaces you'll might want Confluence. If you want community development in an unstructured manner, you want MediaWiki. If you want separate webs, structure, but also community development, go for TWiki - and then reskin it.