Okay, since we can't decide on Steel or Ice, why not both?
Terrakion @ Choice Band
Trait: Justified
EVs: 4 HP/ 252 Atk / 252 Spe
Jolly Nature
- Close Combat
- Stone Edge
- X-Scissor
- Sacred Sword (Or Rock Slide if anyone really wants to argue the filler)
CB Terrakion is the premier wall-breaker in OU. But you probably know that already. Besides that, Terrakion gives us the powerhouse we need to take down Steel and Ice types without an issue. The only thing we have to fear is Mamoswine- but it's horribly slow, and I'm more then confident a decent player could realize all they have to do is switch into the Ice moves aimed at Dragonite. Terrakion also can deal huge amounts of damage to phazers pretty reliably, with even Physically Defensive Hippodown struggling to do anything other than click Slack Off. Terrakion and Dragonite also have generally good synergy, wuth Terrakion resisting Rock and Ice and Dragonite being immune to Ground and resisting Fighting.
Terrakion cannot switch into anything Mamoswine uses except Stone Edge or Stealth Rock, since Rock does not resist Ice.