Earthquake is better on normal Metagross. However, Mega-Metagross have the ability 'Tough Claws', so the move Hammer Arm might be considerated..
Both have their own coverage too. Like Hammer Arm covers Dark-type and Earthquake covers Fire-Type, and they both covers Steel-type.
Earthquake can deal damage to more Pokemon, but Hammer Arm deals more damage but more Pokemon resist it, so which is better?
Here the moveset :
Metagross @ Metagrossite
Suggest other moves to be replaced too.