Suramar

For those rushing for the transmog, the fastest way is to complete the achievements "Tour Suramar" and "The Nightfallen".

You should first unlock world quest before doing this as world quests give 2000 rep for the faction of that zone per quest.

Follow the main campaign while doing "Tour Suramar" along the way. For some unknown reason, I got a 2000 rep token from a chest near the zone of the city where you get your disguise. Might be pure luck.

Keep following the campaign and spend the rep tokens earned along the way. Do all the world quests in the zone. Note that some world quests are locked behind the campaign.

Got the achievement with the 7.0 campaign at around 80% progress and no side quests.

You can knocked out the Nightfallen achievement by making a Nightfallen character.

This has not been my experience, or perhaps I am missing something. I did a few world quests, one gave me 50 the other gave me 0. I have not been getting 2000 per quest, unless those world quests unlock later on?