Hello!
I was torn between oxford and cambridge, now currently studying french at oxford so feel free to pm me for further details!
My experience of the oxford course is to be very literature-based. There's a fantastic range within those parameters, but that is the primary focus. I don't believe this is the case at cambridge- I went on a language open day there and they suggested that you could do papers in all sorts of areas- literature, periods of history, and society too. Also, the cambridge tripos system is much more flexible than in Oxford, so you can also change subjects and do different papers through there.
Also, at cambridge, I think it's classed as 'MML', whereby you have to do at least two languages. In contrast, at Oxford, you study 'French' (and another language if you want to). This means that, in theory, you can switch languages about/change up your percentages at cambridge, but at Oxford, it's more set in stone. Maybe someone doing MML at cambridge can clarify if what I've said above is correct?!
I think, course-wise, I much preferred the sound of the cambridge one.. I ultimately chose Oxford just because something about it meant a lot more to me than cambridge did- difficult to explain! That isn't to say that the course at Oxford doesn't have its merits, too- the amount of literature you can study is fantastic, obviously, and I'm sure you would enjoy the rigorous approach to language teaching. Also, 'literature' doesn't just mean novels- there's poetry, plays, and philosophical texts, too- I've chosen to do lots of the latter, as it interests me the most. You can navigate your way around (to some extent) the things you do/n't like. There is also quite a lot of scope to do linguistics at Oxford as part of a language degree.
Also, check out the modern languages handbooks for Oxford and cambridge. Here's the link to the Oxford one:
http://www.mod-langs.ox.ac.uk/handbooks It details the exact specifications of the course. 'Prelims' is first year and 'FHS' is second and third year (there are no exams in second year).
Just google til you find the cambridge one.
Hope that helps somewhat- take your time... ultimately the course is what you will be doing for the next four years so choose wisely!