Dalaran (Northrend)

EDIT: Easiest way to get into Dalaran (Northrend) after Dragonflight launch, there is literally a portal in the Orgrimmar portal room to Dalaran in Crystalsong Forrest, that is the one you want.

Easiest way of getting into Dalaran (Northrend) after the launch of Legion (Patch 7) from the new Dalaran:

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2. Use your Dalaran Hearthstone to get to Dalaran (Legion)
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4. In Dalaran (Legion), take the Portal to Vale of Eternal Blossoms
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6. From there, fly to your faction's Shrine/City (Alliance/Horde)
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8. The portal inside still points to Dalaran in Northrend
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Alternate method:

1. 
   
2. Use your Dalaran Hearthstone to get to Dalaran (Legion)
3. 
   
4. In Dalaran (Legion), take the Portal to Wyrmrest Temple (Dragonblight)
5. 
   
6. Fly or take the flight point North to Dalaran (Northrend)
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Fastest method:

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• The fastest method still remains using your Ring of the Kirin Tor, but obviously requires that you have one. These old rings still point to Dalaran (Northrend), which basically makes this a sort of Hearthstone that you can buy if you come here often.
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EDIT: To know where your factions cities are in Vale of Eternal Blossoms, here is a question on Stack Exchange to see where they are.

EDIT: These methods (apart from the ring) will require you to be of appropriate level to have access to the portals mentioned above, which should all be there if you can get to new Dalaran (Level 100+).

As of today (3/13/2019) I found that many portals have simply vanished. I am doing the hunter quest chain which requires several visits to the Storm Peaks in Northrend. I found the way to go now as Horde is to get to the new Dalaran, then take the portal to Orgrimmar (the only one in new Dalaran now that I could find), and that portal now takes you to a new portal room in Org which contains a portal to the Crystal Forest in old Dalaran. Don't know why everything needs to change, but there it is. Happy hunting!
Edit: Or you can just go to the front gate of Orgrimmar, and take the passage down to find the new portals. Duh.
Edit 2: For Alliance, simply go to the mage tower in Stormwind. Lots of portals there now.

The easiest way I've found is to take the portal to Wyrmwrest Temple from new Dalaran and then fly or take the Flight Master north to Dalaran (Northrend)