Which ares to use

Sucks you got these IVs, but go with the -def +res. Ares needs as much attack he can get to abuse Draconic Aura or AoE specials.

That really depents on if you want to use him in player phase or enemy phase

With the extra speed and more defence, Ares -atk+spd will be able to avoid doubles and maybe even double some slower enemies in return (with horse buffs).

The -def+res is basicly neutral. He won't be oneshot by most physical units but he can't take much more magic anyway. His high atk and weapon will do their job, be sure to pick up vantage to destroy the enemy with his specials.