I think it doesn’t really matter what pre-IB programme to take because the content remains fairly similar or even identical. With that being said, any programme would prepare you for the IB.
I studied Cambridge IGCSE before embarking on my IB journey, and there isn’t too much of a big leap in the content. However, I think it is definitey useful to have taken subjects which you would continue to take in the IB (ie. IGCSE Biology if you’re planning to study IB Biology and Maths and Additional Maths for IB Maths HL/SL).
For me, the biggest change when transitioning to IB from IGCSE was having coursework. My GCSE experience was that it was very exam-based. Although there was an option to submit coursework for subjects like English Literature , Geography and the sciences, but most schools opt for non-coursework options meaning your entire IGCSE grades are based upon the final examinations in May/Jun or Oct/Nov.
The MYP (Middle Years Programme of the IB) in theory therefore prepares you better for the IA, ToK, and EE parts of the IB. But if you’re diligent and hardworking, you should not really find it challenging because your teachers are there to guide you and you can always look up resources and sample work online. On the other hand, IGCSE or other programmes would allow flexible subject combination that help you explore your interests (I took English, Chinese, Maths, Biology, Chemistry, Business and Sociology).
So to conclude, I’d say the MYP provides a really solid foundation for the IB – which is helpful for those who want to get adapted to the rigour of coursework and internal assessment. But you can always explore your interests prior studying the IB so it’s really up to you!