What is the most common species in the Warcraft universe?

Interesting fact:

Azeroth was originally supposed to be a rather dark place at night, like, literally! Night time was intended to be so dark that players couldn’t see anything and Duskwood was one area in particular that was supposed to be completely dark. Players would have to light their way through it with torches built via learning the Survival profession. Or hanging around with those who had the necessary skills. Could have been quite interesting, huh?