All save data is backed up to the cloud servers for all users and will automatically sync when you load a game on another xbox. Of course if you've got a game like Forza5 with massive save data that's bit of a ball-ache.
Otherswise, it's as @oscar__explosion says, you need a 256gb+ usb drive to move data to.
I think people are kind of missing the point of the post. The frustrating thing about the ending, and even as someone who picked Option C I say this, is that it's cheap. It's cheap to give the player this morally grey dilemma, and then decide to make a canonically all-around good-in-every-way ending out of one of those choices. Jeez guys, think about how much time the average player is spending just on the main plot. Like, at least a couple days of solid gameplay. Yet the ending, the bow that wraps up the whole product, rests on a flimsy moral choice which is less a moral choice and more a "can you figure out the right answer?" It's weird, and I find it kind of lazy.
Edit: Damn, you've nailed my issues with the story ending as well. They make all the noises of there being character growth but buggered if I could see it.