One of the cool additions from Shadowlands is the ability to travel between timelines (expansions) using Chromie. If you’re looking to level primarily through questing then your options are - The Warlords of Draenor timeline has excellent quest density. Each zone also features one-time bonus objectives that are reasonably quick to complete and rewards oodles of XP. - Legion also has great quest density which cuts down on the amount of time you spend running around. It’s also more fun to play than Warlords of Draenor. - Battle of Azeroth isn’t quite so good for leveling but is a little more beginner-friendly. Consider it if you’re new to WoW.