Other interesting discussions about language usage on the AP blog - http://blog.ap.org/
'Leaker' is the closest thing to neutral. With most people he is either a 'whistle-blower' or a 'traitor'.
Hmm, this makes sense, but I think they need to find a new neutral word - leaker seems to have moved significantly closer to "traitor" than to "whistle-blower" amongst most of the people I talk to.
Because that would be taking a stance on weather he was a whistleblower or a traitor. He leaked the documents, so he's a leaker.
In my country is worse. The media call him a mole.
Well, he admitted to as much. I think the only reason they don't call him a 'mole' in the U.S. is that he isn't still there and that is identity is known.