Realistically how many Mewtwo?

Trying to figure out before the transfer bonus ends how many Mewtwo I realistically need to keep/build since I know it shakes up the meta for a few types. Seems mega mewtwo Y is the top mega attacker in psychic, ghost and ice types. That being said, can I just build one Mewtwo Y with psycho cut/psy strike and put a third ice move on it? Is shadow ball mewtwo worth the etm, doesn't seem like it would be to me. And no need for electric type mewtwo since raichu released? And what about mewtwo X, is there any reason to have more than one with counter? Any advice appreciated, currently have 5 Y and 3 X but if I can transfer some of these and get the candy bonuses would be nice.