Right away my mind goes ETHEREALS!!! However, I have to say that if they were a playable race I would probably get sick of them because everyone would have one. Same with if they ever did Murlocs. Well, that’s not necessarily true because I’d have less Murlocs than I have Blood Elves (click on Faces along the header to see what I mean). The Vry’kul would be another popular choice for me, as it’s another race I’m quite fond of. But if I had to base my answer off of what could actually work as a player race, I’d have to choose the Tuskarr.
Now don’t get me wrong, there are several races I would love to play before the Tuskarr. But I’m trying to look at it from the perspective of existing lore and what would make the most sense. I think the Quillboar would be near the top of my list but they just don’t make sense with either faction. At all. The Tuskarr do. Heck, they could’ve easily been the original Pandaren.
Given the way Northrend is set up, they could’ve been the game’s first neutral race. One tribe could’ve gone to the Horde and another could’ve gone to the Alliance. I can easily see Hunter, Warrior, Priest, Death Knight, and perhaps Shaman. Give them a racial bonus to Fishing and Swimming and you’re set.
As I said, the question is a bit of a hard one for me because a number of races just don’t make sense. Choosing something that I would really want, like perhaps Naga, that just doesn’t fit would be like Blizzard allowing Forsaken Druids or Draenei Warlocks. Given the context of the game, that just sounds bizarre, nevermind how it would work within lore. My head’s trying not to explode just thinking about it and the same thing applies to the other races of Azeroth. At the end of the day I think the Tuskarr would be the best choice out of the NPC races.