I don't know if this is breaking MN protocol... there was a post on this a year ago (which you might want to look for), and I'm pasting in my reply as I'm too lazy to rewrite!
If your goal is to give your DD an excellent education, the IB is well worth considering. The three Higher Level subjects are at A level standard (some a bit lower, some a bit higher, but overall roughly equivalent), while the Standard Level subjects are a shade higher than AS Level, and result in a very well rounded education. Plus, there is the 5,000 word Extended Essay research paper and 2,000-word externally assessed research papers in every subject, which mean DC arrive at university very well prepared and well organized. My understanding is that IB students do better than average at university as a result.
IB is also a good choice for students who aren't ready to narrow down at age 15. My DD could have applied to study a range of humanities or biological sciences at university.
BUT... if your goal is to minimize stress and get your DC into the best possible UK university, I would steer clear of the IB. On the stress front, there are the CAS (Creativity, Activity and Service) hours that make for a well rounded, community-minded person but take up a lot of time. Then there is Theory of Knowledge; yet another course and yet more work. Plus the fact that students are carrying six subjects, often with at least one where they have little aptitude, plus that 5,000 word Extended Essay, 6x2,000 word pieces of submitted coursework, oral exams in a host of subjects (not just languages), plus..... It is a very heavy programme.
For universities: One mediocre grade in a Standard Level course that is not remotely related to your DC's future plans (in my DD's case, maths) can pull down the whole average, making it difficult to hit those conditional offers. And IB students are competing for places with A Level students, who are generally taking far fewer courses and only in areas of strength.
For medicine, IB students simply cannot take three sciences and this can be limiting. DD's friends had very limited options for medicine despite being top students. And in my humble opinion, many UK universities do not properly value IB and have requirements that do not equate to what they require for A Level (unlike Canadian and US).
Hope this helps.