Wikidot has a simpler user-interface, loaded slightly faster when I tested it and admin access allowed me to freest and edit permissions as well as set site admins. The control over its navigation is also easier and it lacks the visual editor, which will push focus on content instead of the sit, which really is just a catalyst. Both Wikidot and wikia use wiki source code and have larger communities, but only Wikidot lets you mitigate some of that to selectively choose what is more beneficial.