I would have to say Java. Between the tutorials, Language/VM specification & library Javadocs, it's the most thorough I've seen to date...
Do you mean formal documentation, or all documentation (including sources like stackoverflow, blog posts, etc)?
I haven't used Java in a while, but my experience lately with Python docs (both formal and informal) has been fantastic. This applies not just to the core language and libraries, but also various third party libraries and frameworks.
C# does!
Core stuff, sure. But much of MSDN is a wasteland of autogenerated garbage and super vague shit that is of no use to anyone.