From an RP standpoint (if you actually want to fit your race reasonably with your class) then forsaken is a no brainer. Even the new Touch of the Grave just feels like a shadow priest / warlock type of spell.
Racial bonuses are nice and all, but to be honest I actually want to make my character believable in the world. If my class is evil, then my race should be evil. If i'm a gnome, then i'm doing gnomish engineering etc. I don't RP at all, but I still respect the rightful order of things.
All current race/class combinations fit in with lore. You just need to read a little about the background of every choice to understand it's place. Priests are not good or evil, no class is strictly good or strictly evil no spec is strictly good or strictly evil. It's the choices you make that determine your alignment. Who's to say that a gnome can't learn Goblin engineering - in fact, it's a much more interesting personal story if that is the case.
What's the story if you learned gnomish engineering as a gnome? You went to school, studied engineering, the end.
I think you missed the part where I said I don't role play, but anyway. Shadow Priests*** (not holy, not disc) to me come off as an EVIL specialization. You have a spell called death, devouring plague, pain, dark archangel. That just sounds mean. Forsaken in current lore definitely mean (they are indeed raising undead throughout the expansion). So you want to hurt people? Infected then with harsh diseases and be all shadowy? forsaken!
But to be completely fair, my actual point is that people shouldn't just pick races because they have an OP racial. Pick a race because they reflect you as a player and because you think it'd be fun to represent them. There's nothing wrong with being a Spriest tauren if you think that best reflects you. Just don't pick ONLY because of a racial bonus.