Which has the better course for what you're interested in? Or research, teaching? How about the colleges, student life and traditions?
You might get some better results posting in the Oxbridge forums for there specifically, or adding it to your title. All unis will have similar core modules due to BPS guidelines, but the way they are taught can be quite different. It would be worth going to open days for both to see which you like the feel of, or even just a walk around the cities and any open colleges.
Be careful placing too much weight on optional modules and staff members etc, as obviously they are subject to change. As are your interests as you go through uni! But they can be a rough guide if there's an area you particularly want to go into.