To give you some perspective I leveled both a LF Ret Paladin and BE Rogue (so one started from level 20 and the other from level 1). I focused on getting the achievements I was missing for the Loremaster, so not the most efficient route by any means. I was using full enchanted heirlooms (minus the ring) and the WoW-Pro addon though, as well as having War Mode turned on all the way.
What can you find in our WoW guide? We decided to approach the matter a little differently than usual and instead of preparing a comprehensive guide we focused on major features and key information, tips, and instructions, which may be useful during leveling up and raids. Therefore, instead of providing a detailed walkthrough, we've included answers to important questions, such as how to unlock a mount, how to reach new locations or, most importantly, which allied race you should choose at the beginning? In other words, in following chapters and section you can find everything that will be useful for a beginner player during his adventure with WoW's new expansion.
“That’s the impetus behind everything, is to just make sure that players feel like things that they do in the game will have great consequences or great victories or whatever it’s going to be, right? Ultimately, our job is to create a world and environment and mechanics that support all that stuff. And however the players choose to make their choices is really up to them.”
Level 120 comes and goes. Island Expeditions have unlocked, but it turns out they’re not much fun, and the most rewarding versions are only accessible to premade groups. You turn to Warfronts only to realize they’re not available this week. Fine. You can always grind out better gear. Except as you do, you notice your new gear has higher Azerite requirements than your old gear, which means your shiny new items have fewer unlocked traits than what they replaced. Discouraged, you decide to roll as one of the cool new Allied Races. Except you can’t because they’re all locked behind reputation grinds.
With G'huun's threat eliminated, the Horde and Alliance return their focus to the war. While the Horde procures the Scepter of the Tides, a legendary artifact capable of controlling the seas, the Alliance dismantles a potential alliance between Sylvanas and the vampiric San'lyan Elves. The Alliance begins to gear up for a preemptive strike against Zandalar, with the goal of crippling the Golden Fleet before it can be used against the Alliance and driving a wedge between the Zandalari and the Horde.
Heirlooms are special pieces of armor that level up with your character, so they have stats that are always respectable for your character’s level (up to level 110). Heirlooms that fit the head, shoulder, chest, legs, and back armor slot offer an experience bonus. The total bonus is 45 percent if you have them all. It’s also possible to acquire a ring that adds another 5 percent, but you must win a fishing contest acquire it, and that can take some time.
Anyway both got to 110 at around 50h played. I messed up with my Pal by going to Legion once I hit 100 instead of finishing treasures and bonuses in WoD. All in all, if I picked the best zones and was only trying to level as fast as I could, I would probably could have done it in roughly 40h. Note that it would have a been A LOT faster with a Monk as both Ret and Rogues don't really have a decent AoE until 40+ (45 for Ret and 63 for Rogue I believe). The daily also helps a lot. I know that leveling my Monk before the pre-patch was insanely fast. Might be slower with the changes to FoF, however.
For reference, my previous best time abusing Method-0 in 7.3.5 was 32.4 hours(as show in the old thread). A difference of just over 8 hours; which isn't all that bad, all things considered. And I believe I made several errors along the way, which could be cleaned up in future runs. I believe that that gap could be significantly closed by using a monk's bonus, but I hate playing monk...so...yeah. YMMV