I run boomkin with treants for elites and emergencies and it’s worked well so far, cleared Layer 3 yesterday (highest available currently).
The powers that have worked well for me are any to do with boomkin spells, and of course the affinity ones. Having every affinity passively + 100% effectiveness is great, that’s passive 30% move speed from FA, 8% life per second from RA, and 12% DR from GA. The mobs with moonfire do 20% less damage is great for bosses as well.