The standard best practice for REST APIs is to have a hyphen, not camelcase or underscores.
This comes from Mark Masse's "REST API Design Rulebook" from Oreilly.
In addition, note that Stack Overflow itself uses hyphens in the URL: .../hyphen-underscore-or-camelcase-as-word-delimiter-in-uris
As does WordPress: http://inventwithpython.com/blog/2012/03/18/how-much-math-do-i-need-to-know-to-program-not-that-much-actually