This guy is an awesome tank with great HP, Attack Defense, and decent Sp. Defense.
EVs: 252HP, 148 Attack and 124ish spAttack for Psychic
Hammer Arm: He already has low Speed, this is a great Fighting attack for coverage.(100pow, 90accuracy)
Steel move: Either Meteor Mash for Power, Bullet Punch for priority, or Iron Head for accuracy.
Last move: Magnet Rise for Ground Moves, Hone Claws for raising Attack, or Earthquake, Shadow Ball, or Sludge Bomb for coverage.
Great HP, although not as good as Metagross's. A pretty well rounded pokemon.
Try a critical set:
EVs 252 hp, 252 sp defense
Slash or Bulk Up.
Overall, I'd use Metagross because of greater stats(almost 100 more total!) and such a big movepool.
However, you already have a steel type in your team. Your choice.