Originally Posted by
Cyonis
I leveled my priest as disc/holy a few weeks back, doing mostly dungeons. I'm level 102 right now. I specced shadow for the first time at level 98, where you can go to Legion content.
I did quests while running dungeons from outland onwards. Disc is great for questing and great for dungeons too. You will often be top dps as disc. I only went holy when I felt like lazily healing dungeons or the group dps was so high I couldn't do anything myself. Questing as disc works fine. You've got more burst than shadow, probably all the way the up till around level 100, and even then it will only be a little bit behind. Holy can burst very hard too, but the cooldown on the burst is longer, which makes it more akward to use, in my opinion. It does work, though.
Dungeons give a lot of xp, up till around level 68, where a combination of dungeons and quests will start to be better. You'd be best of doing each dungeon just once, even queueing specific if needed. When you reach WoD content at level 90, dungeons will be nearly worthless in terms of xp, and you'll be much better off doing quests. Of course you can still queue for the occasional dungeon, but I would not recommend it.
When you reach level 98, you can go to the Broken Isles. Relog for the quest to trigger. You will need to do quests at this point to unlock world quests for the first time. If you have already unlocked them, it is not needed as much, but you will still need it for reputation.