Do all 3 of the mastery quests at once so you can just run through the area killing whichever ones you see.  I always tried to kill the clefthoofs first when I saw them because it seemed like there were less of them in the area.

These quests end up bringing in a ton of XP when you're done because of all the kills you have to rack up.  Then, you add in the bonus XP for completing the quest and there's the potential to get about 40K XP (with rested XP) for this quest.