Cambridge is generally seen as being more difficult than NCEA in most subjects, but perhaps less demanding than the IB. Similarly, it will open up a wider range of opportunities (especially in the UK) than NCEA will. IB and CIE are recognised fairly similarly in places such as the US. Overall, I think a decision should come down to how much time you’re willing to put into your studies - IB will take up a lot of your time, whereas CIE is more demanding towards the end of the academic year, and NCEA is generally considered as less demanding overall.