Halfway up the mountain is the Triage Camp that has 9 trolls close by. You can quickly circle the area killing all 9 and then change to a new instance and repeat. Due to the camp fire being right next to this group of trolls you don't spawn far away.
You are limited to hopping instances every 2 min but this doesn't slow you down too much. I was able to average 9 kills in a little over 2 minutes.
216 kills an hour based on 9 kills per 2.5 minutes
Location of the camp: