That's a toughies... I am very partial to the races I created for Saggakar: I love their flavor and the fact that they depart from the 'usual' Tolkien tropes.
If I had to give just one, or one of the core races, I would go with human.
Although they are not overly snazzy, they are a good reference point for what other races are good/not good at. I really good average character everywhere.