Out of all the thralls(flame,frost,storm, and dead) which one is the most powerful or are they all equally strong?

I like to use Dead Thralls. You can load their bodies up with junk, and they are a movable container. Plus I can give them better weapons, and have them destroy with whatever I give them. The groaning get's annoying though.

To be honest the elemental ones are all weak as flying crickets in the late game (even with all the support perks). You are much better off going with Dead Thralls (especially ones that can summon stuff of their own).