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:
Original login screen theme: http://www.youtube.com/watch?v=y_uc7MmeyyY
Seasons of War: http://www.youtube.com/watch?v=MwsYfXdhDtc
Stormwind theme: http://www.youtube.com/watch?v=R1XcJIDi1Qs
Durotar: http://www.youtube.com/watch?v=alWTyJr1Gro
Burning steppes: http://www.youtube.com/watch?v=RdZN9Rf1ANQ
Elwynn Forest: http://www.youtube.com/watch?v=uvW-QTiZLQ0
Ashenvale: http://www.youtube.com/watch?v=b4U4vr_Ra3o
Since lot of people are propably familiar with this composer's wow tunes, here is a bit more rare piece that also prove that he's very much capable to still make great music. When he can write music like this and almost whole vanilla wow soundtrack, one could just imagine what kind of soundtrack this dude could make for next expansion: