A levels and IBWatch
In general, if your interests lie in the Sciences or Visual/Performing Arts A-levels usually end up being the better options, due to allowing you to focus on these specific interests better. If you're interested in the social sciences and humanities, IB is usually a good option due to the breadth of knowledge and perspectives it offers.
An example for the former case, it's not possible to take Maths, Further Maths (which is very different in IB and extremely rare anyway) and two Sciences, as is common for A-levellers. Nor can you take 3 Sciences + Maths as some very well prepared prospective medical applicants do.
On the latter side though, for e.g. PPE or similar, many A-level students end up with odd splits of A-levels with like, History, Maths and another which while useful for applying to PPE don't correlate to many other degrees as well as other combinations. Whereas IB naturally includes this combination, so any social sciences student will have a minimal quantitative background, and also offers additional perspectives from e.g. languages. group 6 options, some scientific knowledge...All of which is useful for these kinds of subjects.