I like Zen too and maybe its situational. I find Ana can heal quicker if you have a large health pool on your team (several large tanks are pretty easy to hit and heal quickly). Plus the sleep ability can shut down an ultimate instantly (Genji, Mcree, Roadhog, Reinhardt) Im not the best aiming with Zen either but maybe I should give it another try. The discord orb makes a huge difference and maybe I wasn't using it to its full potential before. Good luck out there!