@Woodpecker22
I did IB 20 years ago and it was pretty tough. My peers which would have easily have got 3 A at A level did not get high enough IB scores for their Oxbridge offers which in my opinion were unreasonably high. Some subjects were a lot harder to get full marks in than others (as it depends on the internal standard). No one in my IB class got full marks in higher maths or physics.
Having said this I was glad I did it because of the well rounded experience it offered and it does set me apart from others.
At the time my main reason for choosing it was because I could continue with 6 subjects and I didn't want to narrow my options.
Second this, I also did IB some 20+ years ago and it was much tougher for IB kids in my school, than for those doing A levels. Academically speaking I still believe it is superior to A levels.
But, you have to take into account the circumstances:
1- Officially there is no discrimination between IB and A-levels, but the conversion by Oxbridge was far from generous at the time. In our case, IB was the great leveller as most smart kids picked it.
2- Take two kids of the same level, the IB kid will divide his attention amongst 6 subjects, whereas the A-level kid will focus on three. It goes without saying that the A-level kid will have a better chance at Oxbridge, whereas the IB will be better recognised globally.
3- You will probably not know better what you want to do in life at the age of 18 than at the age of 16 at least I didn't. My sister chose to study economics at the age of 18, only to announce that she'll want to be a medic at the age of 21. To get additional perspective at the age of 16 you'd need to change your environment e.g. new school in which case it may be worth to pick IB.
4- At the age of 16-18 there is a lot going on in a teenager's life. First love, driving license, holidays with friends, etc. It's a very good time to cut the slack and rationalise.
There are plenty of good arguments in favour of IB. It is clearly the more academical choice, and in an ideal world of no distractions and fair conversions, we should all choose that. It is better if you believe in intellectual superiority and learning is for its own sake, and one could argue it has better for prestige (in reality noone cares, as the uni will overshadow that)
If you're purely result oriented, aim for UK schools and looking to get the biggest bang for the time invested, then A-levels is the smart choice. If you like intellectualism and academics for its own sake, then IB is the better way. Both can be risky, albeit for different reasons.