I have children who have successfully applied to both. It is a very personal decision but some of the factors that have been important to their decision making are:
1. Comparing the courses in terms of compulsory modules, options, timetable (many Cambridge courses have lectures on saturday, for example)
2. Size of town : Cambridge can feel crowded in the centre , and Oxford less so, particularly for colleges to the North of the city
3. Flexibility in the course: Cambridge courses like natsci, hsps etc can provide more time and opportunity to experience new topics before settling on areas of real interest. Oxford courses are more discretely defined. For my children who didn't want to specialise too early they chose Cambridge whereas the ones already really confident of their preferences chose Oxford. E.g. Natsci vs biological sciences.However, Oxford have more joint degrees so you may be able to pursue two interests there when Cambridge would require you to select, e.g. contrast PPE with economics or Maths and Computing (Oxford) vs just Maths or just Computer Science (Cambridge, at least from second year onwards).
4. The structure of the admissions system as there are key differences. Oxford interview fewer applicants but have generally lower offers so, providing you receive an offer, by the time you are sitting a level exams you may be much more confident of making it. While the overall stress of the admissions process seemed similar, the distribution of that over year 13 was different for the two universities, especially so for courses which required STEP ( maths but also engineering at some co colleges) . This is a very individual preference and you have to work out what would be best for you. Certainly, for one of my children the uncertainty created by a STEP offer made Oxford the preferred place because that child placed a high value on having a reasonable certainty about which university they would be attending at the end of A levels.
Factors which were not relevant:
1. Perception of how easy o r how difficult to obtain an offer
2. College - there is huge variety across both and around one in four offers at both unis are to a college other than the one applied to.
3. Which ones their friends were applying to.
4. Employment prospects , student satisfaction etc as these data reflect so many other variables
5 The views of their parents!
As a postscript, both universities offer a tremendous educational experience with unrivalled opportunity for small group teaching and access to a huge array of resources. It really is a privilege to study at either. In exchange, the courses are tough and may feel very demanding and you are likely to have to work very hard. At times it might even feel overwhelming! Not all my children have finished but none of them have ever regretted choosing one over the other.