Hammer Arm as it provides allot of coverage for his tier and in general.
Psychic isn't the best option because it is a special move and the metang family are far better physical wise and you will find a zen hedbutt will do far more damage than a psychic.
Though if this is infant and you lack a psychic typed move, then go psychic as it gets stab so will do more damage than hammer arm, but then again if you have a psychic move use hammer arm.
