First up we have patch 7.3.5, which was implemented several months ago as a major shakeup to how leveling was approached. Instead of going from low to high level zones like the way the game had always operated, Blizzard opened up the map with more of a Guild Wars 2 type system -- you now have more of a choice of where to go with a scaling mechanic. But when combined with 8.0's massive stat overhaul, things got murky.
Welcome! While this leveling guide is specifically made for the class and specialization(s) listed, we also have a general Battle for Azeroth leveling guide that focuses on the specific features of the Battle for Azeroth expansion including preparation of your mission table that will be used to unlock new areas, progressing on your faction's War Effort to save time at Level 120, and a reminder to keep ALL of the gear you find for the Scrap-o-Matic 1000 or Shred-Master Mk1, which will greatly increase your resource generating capabilities. Please visit our 110 to 120 leveling guide for this information and more (including Heirloom and War Mode advice that also applies to players who are not yet Level 110.
Lastly: The zone order I recommend for Horde is Vol’dun- Zuldazar- Nazmir. Vol’dun is definitely the most challenging of the bunch and having the use of your Legion gear and leggos will smooth this zone out. Nazmir is the easiest of the bunch which is nice when things start to get a little grindy past 116. For Alliance, I recommend Drustvar- TS- Stormsong. Same logic as the Horde side, in my opinion Drustvar is the hardest and Stormsong is the easiest for when it gets grindy. I would recommend you waiting to do any of the War Campaign until you are capped because it just takes you out of the way. I also recommend not killing a single rare mob or picking up a single treasure because in my experience it is just not even remotely worth it. The gear scales up on the rare mobs so its smarter to keep them till 120 anyways. After you are done leveling, I do recommend taking the time to do all the quest at the Faction Outpost in your enemy territory. They do provide rep for the Honorbound which helps. Most of them are quite easy. If you do not level in Warmode, you will usually hit 114 from your first zone, 117 from your second, and cap 120 about 2/3 in your final zone.