We can't really answer that for you.
Do you like FPS? That's what this hinges on. If you don't, don't even think about getting BC2. If you do, consider which of HR and BC2 you'll enjoy more. They are completely different.
Obviously, if you want a multiplayer game, get BC2. But if MW2 is the only online FPS you've owned, and you hated it, get HR.