For defense with tank position:
I did not get Azlar to 4-80, because of getting Anzogh and having Isa already. I tried several defenders and Isa seems to be the one least attacked and keeping me highest. Azlar should not be too far away from stats and skill.
Then I thought Anzogh was a healer and got him to 4-80, but his heal is low. Defense against one color is one of the weakest skills. And as a tank, he is attacked more often and more successful than Isa so far (both in a colored team with fast snipers to the sides). So, I only use him for farming.
I have not used Frida as tank, only tried her for that tournament without green color. There I got 2 wins and 8 losses from Frida which is really bad. But that is statistically less helpful. I can’t imagine Frida as a good tank.
Richard is quite solid as a tank and maybe the better of the four. But as you can see from the answers so far, all four are not the best tanks.