With the introduction of multiclasses, there isn't much of a difference, but if you want to play a pure class, I would recommend Nightblade, it's easier, you don't need to focus on corpses

Outside of very high-end raid content, that has gatekeeping, any of the classes.

All classes are getting a rework (so far only DK), so it's hard to say for the future. But if I had to choose between these 2 I would say NB is the better option (because of the corpse stuff).

Personally I have 2 of each base class and 1 of Warden, Necro and Arcanist. This way I could try them all out or have a character ready when things change.