Poll added, it's a difficult question though. I think I'd probably take the 2:2 from Oxford but that's principally because of the other opportunities that I suspect I would get from going to Oxford. However if the universities were more closely matched and it was say a middle-tier ranked university then I'd take the 2:1.
As some other have said a degree is often simply a way to prove that you can learn up to a certain level and a way for you to access options more easily than otherwise. In some ways it's a shorthand for employers to be aware that you've probably got YY level of ability and it roots out a number of candidates who don't meet that requirement. It doesn't prove that you'll be good but it's an easy substitute to thoroughly testing you themselves.
As it is I've got a degree from a university that doesn't have a particularly great reputation, the course itself that I did isn't too bad though as it's ranked as the best modern university in Scotland for it. That wasn't even a consideration when I went there though as I went for a different course but looking back I'm fairly happy with the way things turned out. For the little it is worth the graduate scheme I was on has entrance requirements of a 2:2.
//edit hold on a second, I'll sort that poll out.