Airborne Tumbler

If you wish to get this achievement done in around 30 minutes have a battle.net friend hop on a player of the opposing faction, place a skull on their head (Target Marker Icon or /run SetRaidTarget("target", 8) . Chose a nice open area, I suggest [/way 62, 83] in the waking shore, a large body of water you can fly back and forth, and this way, you can use Whirling Surge into them (without your visuals obstructed by trees or other clutter). Every 30 seconds on cooldown, using this method, I was able to get all 50 in around 30 minutes.

You can hit more than one person at a time. Good places would be Tyrhold, Elemental Storms, Grand Hunt, the pvp world quest boss area

Spot I used to farm this, was "How to Train Your Protodrake" world quest. Lots of players in a small area using their dragons to carry protodrakes to the quest spot. Pretty easy to park on a cliff and dive in for the dismount.