All ways are viable. You can quest, dungeons or grind. I don't really do many dungeons, considering I'm multiboxing, and if I do, I do them when they are green.
I personally just do the kill quests for each zone then Iusually go grind humanoids for money and cloth until I am high enough level for the next zone. Sometimes I grind specific things I need for crafting and my professions, like recipes or materials that certain mobs drop.
The best grinds are the ones with quests associated with them as well. Your best bet is to go to desolace, do most of those quests and then run down to feralas, which you can pick up some quests and grind. Here is where I grinded/quests from 39-42, before I went to tanaris and started getting rep with gadgetzan and owning the cove. There are more quests that I did there as well, but It was mostly just killing ogres, yeti's and furpaws. Also do the escort quest in the yeti cave whenever you find a beacon from grinding. There are 3 beacons you need and once you turn the final one into Booty Bay you will get a trinket called rune of the guard captain, which is extremely good for and physical damage dealers and a mechanical chicken. One beacon in feralas, one in tanaris and the final one is in the Hinterlands. That is also the order you want to do them in, 42-45 tanaris then 46-48 hinterlands. (With some STV, Badlands, and Searing Gorge sprinkled in here and there, STV and Searing gorge are high traffic PVP zones though Badlands is ok, but far away from the primary zones.)
This post was edited by cyberbluntz on Sep 18 2019 07:45pm