Originally Posted by The End

If I were you, I'd buy it off of steam. Then try and see if you could get a CS rep from origin to add it to your origin account. There's no guarantee that you'll get somebody to add it for you, but from what I hear some people have been able to get them to add it for them. And you'd have to go through the same process to add it on Origin if you bought it off of Amazon.

Of course, if you buy it from Amazon, you also get a copy that you can play outside of Origin. They also have a policy of granting new keys if you run out of activations on a game with activation limits. So there's that to consider as well.

EDIT: hadn't refreshed the page in a few minutes. Didn't see that you already made your decision.