I do not recommend going for TBC, although I remember Hellfire peninsula to be decent, everything else is rather slow. Instead go for WotLK, Borean Thundra gets you levelled very fast, and then you can head straight for Icecrown at 67, which is also insanely fast, although admittedly has a few elite quests. You can go to Sholazar Basin alternatively. 2 zones should get you 60-80 no problem.
Set sail for the previously unmapped isles of Azeroth. Battle in groups of three as you race against cunning rival intruders—or enemy players—to collect the island’s resources. Constantly evolving challenges await as you traverse frozen landscapes near Northrend, open the mysterious gates of an abandoned Gilnean castle, navigate a war between elementals and more.
Taking Herbalism and Mining as your two professions can be a lucrative way to level with the very stable and high prices of herbs and ore thus far in BfA. While rested, each mining and herbalism node will award nearly 4,000 experience points which makes it so that four to five herbalism or mining nodes is equivalent to one quest. If you have the Sky Golem mount for herbalism, you can pick herbs without losing mount speed. There are also enchantments for gloves that will increase the speed at which you can process the herbalism and mining nodes. These can be made rather easily by an enchanter and should be relatively inexpensive on the auction house. These enchants will pay for themselves with the time saved while herbing and mining. Remember to continue completing mining and herbalism quests while leveling up to increase the yield of each node making your herbalism and mining leveling experience exponentially more lucrative.

Let’s start with the basics. At its core, World of Warcraft is a saga that centers on two warring factions: the aforementioned Horde and Alliance. They’ve been fighting each other since the days of MS-DOS, locked a never-ending war—save for those rare moments where they attempt to team up to counter a greater threat—that has taken them across continents, into space, and through time.
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.
If you've been away from WoW for some time, you may not know that the game's Legion expansion focused on powering up an impressive "Artifact Weapon" throughout the duration of the expansion. In short, players have been using the same weapon for about two years now. Artifact weapons were pretty cool and bosses did drop Relics which were used to upgrade them. But after two years of using the same weapon, many players are looking forward to the thrill of having an actual weapon drop off of a raid boss again.
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