From what I have heard (and this is just what I have heard from usually reliable sources), the Malaysian Authorities (who have primary legal right to the data) have agreed that it will be accessed by the Australian Transport Safety Board, the (US) National Transport Safety Board, and a Chinese authority I can’t remember the name of. I suspect it will be primarily accessed by the ATSB simply for convenience (Australia’s facilities are closest), unless the recovery is complex in which case the NTSB are the best in the world for difficult data recovery, but the Malaysians would have the legal right to insist on doing it themselves.
Australian Prime Minister has said he is going to speak to Chinese Premier this evening out of respect for the Chinese dead (the PM is in China at the moment) before making public comment.