You can visit AlteredTime for this info but basically
I would say
Alliance - Draeni or Dwarf
Horde - Orc or Troll (Troll if you plan on Arcane)
You need to take into account that the Difference are not big around 0.5%-1% diff for Fire and Frost
but at the moment the Sims for Arcane show a relatively big difference where Troll reign supreme at Orc is 1% after and Dwarf another 1% after and then all the rest with another 1%.
They are all amazingly close DPS wise. If it was me I would go Human. Very nice racials for PvE/PvP. Diplomacy is amazing, Im not sure how its still 10%. Plus, Human always looks good in pretty much any armor and on any mount.
Pandaren sim extremely well for Fire, surprised no one mentioned them. They have the added bonus of also just eating a different food and suddenly being just as good a boost for arcane or frost as well.