What are your GCSE grades like? Oxford selects you on a sliding scale based on your A* percentage and your BMAT results for interview (if you have 100% A*, you have to be in the top ~60% of candidates in the BMAT, if you have 90% then ~55% etc etc. Not sure of the exact percentages and there are some people who still get an interview even if they miss this auto-threshold), so if your GCSEs are not that strong then think twice about Oxford.
On the other hand, if your module results aren't fantastic at the end of Year 12, Cambridge can see your UMS while Oxford can't - that's another factor to consider.
If I recall correctly, I think Cambridge does full dissection while Oxford does prosection.