Should I get Batman: Arkham City or Assassin's Creed Revalations?

Im not sure which game to get for the Xbox 360. Arkham City is already out and seems like a fun game but Assassin's Creed Revalations trailer looks beast. The brotherhood was a real good game to so I need some opinions.Should I get Batman: Arkham City or Assassin's Creed Revalations?
I would recommend Assasin's Creed: Revelations, because its more sandbox AND the storyline is longer, so you will play it for a while. As you may have already noticed with Assasin's Creed: Brotherhood, it will never bore you. I'm not saying that Batman would, its just that Assasin's Creed would be my obvious choiceShould I get Batman: Arkham City or Assassin's Creed Revalations?
ASSASSINS CREED!!!!!!Should I get Batman: Arkham City or Assassin's Creed Revalations?
Why not save up for both?

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