What class should I be in WoW?

I just got a subscription to WoW and I'm not sure what class to pick. I know that I want to play PvE, have Horde as my faction, have Undead/Forsaken as my race, and I'd like to be either a Tank or DPS player. I'd also like to level up fast but it's not a priority. Which class would be the best fit for me?