I completely agree that "Contents" is probably the best title to use for WE.
Agreed, contents seems like the best choice for WE. In addition to WP, a number of other wikis use Category:Contents as the top-level, although I think Category:Categories is maybe more prevalent.
"categories" might be more prevalent, but I have been doing a lot of thinking about what our target audience needs to succeed without having to entirely re-educate them. For instance, rather than calling it the "Main Page" it could be called "home", and "Support" instead of "help" "practice editing" or "contact us". I think that calling it "contents" will tell them exactly what they should understand from it.