Best heavy machine gun for raiding?

Usually I am the back line or medic if you will. I get stuck with the job of rolling defender and picking up those that get caught out of place. As such, I tend to run a rocket launcher to help thin out immediate threat mobs. However, as the player skill level goes up, my job becomes less necessary. I understand that rockets are usually only good in the Kings fall for killing the ogres. But I would like to know what I could use in the meantime. This weeks nightfall was kind enough to bestow the year two Thunderlord upon me, but is that worth it? I don't have the raid heavy machine gun either. What perks are useful?