Who would be best? Jason Hayes, Glenn Stafford, Russell Brower or Derek Duke? I personally hope Jason Hayes, since he was lead composer for vanilla wow and made most of tunes for original World of Warcraft. He came back to Blizzard in late 2012 and hasnt really written that much new music except couple of tunes for patch 5.1 and 5.2.
Some of original tracks that are composed by Jason Hayes

I didn't find the right solution from the Internet.

References:
http://www.mmo-champion.com/threads/1340889-Lead-composer-for-next-expansion

Filtration Video Example