Change class for Heavensward?

[Aeliott]

You should visit the tanking forum. There's plenty of discussion about DRK vs WAR and PLD.

This.

But as for your question, there's not much for us to say other than to try both out and see which you prefer. As for your time constraints - try getting your daily low roulette bonus on DRK which will give you nice chunks of exp (plus the challenge log bonuses, don't forget to commend people!) to help ease that.