These two expansions are virtually identical in terms of exp/h. I personally favor Mount Hyjal, and think it's very slightly faster. But if you know Jade Forest well you can just as easily keep up there. Ultimately you'll end up doing both anyway, so it's mostly academic. Every time I've tested Valley of Four Winds or Deepholme, or any other zone in MOP/CATA's level range, they were worse exp/h. You should not even need to complete both zones to ding 91, so it's more important to just pick one and go.
I remember time when I was at teenage and I used to spend real money for wow gold from some suspicious "hacker" site from China or Korean what ever(note: I didnt spend much). And now I have realized how foolishly I did even I didnt about real money problems in there. Now that I have grown up I have also realized that I was one of those that caused playing problems for those young boys, that they had to play like 24/7 to farm gold for us lazy people.
Special mention is the Darkmoon Faire Top Hat and WHEE! buff. While not always available due to the DMF being inaccessible most of the month, if you happen to be leveling when the DMF is running, it might be worth your time to go and get these. AFAIK they do stack with heirlooms, although I have not personally tested it. Fair warning: These buffs do NOT stack with each other, and the hats disappear after the DMF goes away later in the month(unless you only log in when the faire is running).
Finally: Gearing happens in a pretty linear way for BFA. Once you hit 120, normal dungeons drop 310 and you need 305 item level to start heroics. Heroics drop 325 and I recommend doing Mythic at around 320. Mythic drops 340 and I highly recommend clearing every single mythic dungeon to give you the highest item level going into week 2. On launch, you will have access to 9 Mythic dungeons and there will be 1 dungeon that is gated behind honor bound rep; Siege of Boralus is gated for the Horde and King’s Rest is gated for the Alliance. I am not 100% sure on this, but I do not believe you will be able to obtain enough Honorbound rep to unlock those dungeons with the first week. Either way, its important to get a clear of all 9 dungeons first week to give you the most chances at loot. If PvP is more your thing gear starts at 280 and I am not 100 percent sure how PvP gear works for BFA. I will do more research and fill this in the best I can.
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