Mistarion dropped :o What should I replace?

I opened a few chest to gwt some extra tickets and it just dropped. Which dragons should I pick? I'm thinking replace the green dude which I'm not using very much because they're the same category (balanced/Scale) but use my portal dude along with two of the S tier to upgrade Mistarion and then use Gorgon dude as my new Tank/Shield category Dragon. What do you guys think?