You can outheal healers and out DPS the DPS. Best of both worlds, very hard to take down and very good at doing damage. You have to think about retreating a lot less on a DK.
I know some are saying DH but for me (as Rogue main) they have a lot of the squishyness of the Rogue. Leech only works if you’re doing damage and you just don’t have the armour or the healing power of a DK.
Not talking 1 vs 1 here (Battlegrounds are not about 1 vs 1 imo). I’m talking about when you have multiple enemies trying to kill you. Hunters can shoot you out of the sky when you try to be clever on a DH and fly up into the air with Rain from above.
DKs can take a hell of a beating without having to retreat, which is much more fun than always looking for the escape option I think.