I used fully upgraded and enchanted heirlooms; missing only the fishing ring. Leveling from 1-20 took ~3 hours, at which point I immediately turned on War Mode for the duration. I rarely encountered enemy players, and when I did they almost always left me alone. But the few times I did get ganked, the total cost in time was insignificant. Maybe a total of 5 deaths from ganks in the entire 40 hours.

I had multiple people ask me why I didn’t do blood or prot for leveling on DK/Pally and the god honest truth is the fact that I know how to play ret and unholy quite well and the limits of the class. I tried leveling as prot and good Christ it felt like I did no damage. If you take selfless healer and wake of ashes you should have 0 issues with leveling as Ret and it is significantly faster. As for Unholy if you take grip of the dead to kite a little, deathpact for healing, and keep up with your Dark Succor (spelling?) procs you will have no issues. I died once as DK and none as pally. The only classes I struggled with a little was WW and Shaman. WW because the aoe felt under-tuned at the time and shaman because they are trash imho.

A new expansion unlocks exponentially more powerful gear, letting you easily breeze through Warlords of Draenor dungeons and raids. A great gold making strategy is to solo these challenges and amass a large amount of gold that you get to keep instead of splitting with your group. Start with soloing easy dungeons and work your way towards harder dungeons until you are comfortable enough to take on soloing raids. Speed and clearing ability is key – stick to those you can run through without skipping a beat and you will see your gold making per hour go through the roof.
Make sure you have the two Flight-Path toys purchased, as this can save you time. It won't have EVERY flight path, but will have major locations for faster travel if you need to switch zones entirely(which you will). If you buy the toys on one faction, it unlocks for the other faction as well. So don't spend double the gold! These toys can be found at the heirloom vendor(Undercity for Horde, Ironforge for Alliance)
A good part of the reason it’s taking me so long is the new level-scaling system. Now that zones and their quests scale with the players level, I’m spending more time questing and less time hopping into random dungeons. And with the experience point requirements to level increased for levels 1 to 60, the random dungeons aren’t nearly the level-fests they once were, making questing a much more attractive prospect.
This is also the reason why when I read in WoW forums of people skipping guide sections, due to being too low level I'm not agree and start ranting about it: it'll be a mess syncronizing with the guide and I've seen many people complaining about missing quests or accusing the guide for being innacurate, but not realizing that was their fault since they're skipping and missing a lot of quest chain requirement. Of course this apply if you're following a guide, believe me, it's very frustrating when you remain stuck in a guide section due to the reasons I've mentioned, more than doing grey quests (but they allow to be perfectly in sync with the guide) and goiing here and there to get the pre-requisite quests.
You should try and quest efficiently - pulling several mobs if you can handle it, using your burst cooldowns while questing to kill everything faster. Many people would think that a 10-minute cooldown like Bloodlust is useless in open world, but you can do a "kill-15-mobs" quest in like 30 seconds if you pull a lot and use it. A free quest every 10 minutes is not that bad.

If you bought Legion and have no desire to go through old content, good news! The new expansion comes with a free boost to level 100 for one character. You can buy these boosts from the in-game store whenever you want, but they normally cost $60, so savor this free one. Use it for a class that you are confident you will enjoy. As a fresh level 100 character, you will be able to immediately begin the quest that takes you the Broken Isles, the new region where Legion takes place.
Something to keep in mind as well is that this will make enchanting materials more valuable, since it is likely most players will now simply scrap their boe greens instead of getting them disenchanted. Also redundant dungeon/raid gear can be scrapped rather than traded to the (guild) enchanter in the run. Less stuff gets disenchanted, meaning there will be less ecnhanting materials, meaning their value will rise. All the more reason to DE rather than scrap as an ecnhanter.