I always found it a little boring to only have two playable races in RoM - humans and elves. My gaming philosophy is this: Why play a human (or a race that looks very similar to humans) when I am a human already? I'm already rolled as one irl, might as well pick something a bit exotic.
Now, Runes of Magic seems to have a good variety of npc races already - from the tribal folk in Dust Devil Canyon, the web-y Tiktaalik in Weeping Coast, to the Angren and R'hanka in Northern Janost Forest; and that's not to mention the mysterious large rhinoceros race you find scattered around Dalanis.
If I could reroll my race, though, I think my first option would be a harpy. Just imagine the different color schemes you can come up with for the feathers and talons, not to mention the wing armor that could be available to this race. A good new class for this race could be the Bard, since birds like to sing ;]
The only downside I see by choosing to roll a harpy would be the fact that everyone and their brother would want to roll it as well. With that being said, my safe race reroll choice would have to be the Limon! I have a huge soft spot for dogs, and I just love how tall and elegant the female Limon toons are :D