Brilliant (as usual) episode. I love how the decision came down to who had farther reaching ambitions, in this case, a goal beyond saving mankind, and that Levi was able to make a level headed decision about it. Not that it was an easy choice. It may have also foreshadowed this, but Erwin also has so much blood on his hands at this point, he might no longer be fit to command (in his own mind, already struggling with guilt).