Well all heroes skill as tank is relative to the other choices that you have morning Cups are significantly higher with a GM tank than either Zeline or Delilah… I don’t have Aeron at 80, but my alliance mate does, he does better with Aeron at the helm than GM.
So from my experience (supplemented with someone who has an 80 Aeron)
Aeron > GM > Delilah >Zeline
This post summarizes what I mean by best.