For Alliance it's Lok'Modan, Redridge, Darkshore, Felwood, Stranglethorn (both parts), Plaguelands. Somewhere between 3 - 3.5 of these get you to 60 in like a 16 hours /played, if you queue for dungeons at the same time. I recommend dropping everything at 45 and going to Darkshore-Felwood if you didn't do them yet - they are literally the fastest levelling zones in the game right now, maybe only trumped by Silverpine.
I hope this information helps a lot for players that haven’t had the chance to play Beta and gives you an idea of what you should be trying to accomplish your first 2 weeks of BFA. If you plan on pulling all-nighters, please don’t be reckless and over strain yourself. People have died from lack of sleep. If you want some tips on staying up I recommend taking a nap before launch time, eating a healthy meal full of protein before launch, snacking on fruit and nuts (my personal go to is clementine oranges and almonds) while leveling, if you do decide to drink energy drinks I do recommend not getting the ones packed with sugar (I prefer no sugar no carb Redbull and G-Fuel) and making sure you drink at least 2 bottles of water in between every energy drink so you stay hydrated and don’t crash. A good time to get some sleep is after you finish all the questing and you are 120 which again will take average played 10+ hours. Again, please don’t be stupid and end up hurting yourself over a video game; everyone must sleep at some point, so you won’t be too behind the curve.
Edit 20 It’s been a week since this post and a lot of people are still reaching out to me with questions which is fine. I have had a few different people reach out to me to help make YouTube videos based off this guide and more info in BFA which I’m more than willing to do. Whoever gets the videos up first I will link them here for you guys to enjoy.