Define "best".
Is Perl's Moose better than Python's built-in OO?
It is more complete. Better? Maybe, maybe not. It's very nice, though.
How does CLOS measure up?
Measure up to what? Other LISP object systems, or Smalltalk, and Moose, and Python?
Where do C++ and Java land on the scale?
On a scale of 1 to Verbose, they're pretty far up the scale.
As someone replying to the discussion topic, you may choose any interpretation of "best" that you wish. In fact, that would be preferred, as it would probably produce more interesting discussion than me attempting to rigidly define "best" in order to allow someone to post "given your definition of 'best', language Y is 'the best'".
How about this: which language's OO implementation do you like the best, and why?
Java takes a lot of characters to express an idea. C++ (usually) requires you to take a big idea and break into smaller parts than Java might (because Java has large libraries).