Basically, IB is a curriculum from Switzerland for international schools, 2 years-long programme. The student will choose 6 courses and each course is either into HL (high level) and SL (standard level). There is final exam at the end, and long essay called extended essay to submit.

AP is from US, college/university level courses and exams that the student can take in high school and he/she earns college credits before University.

Roughly if a student is aiming for US universities, recommended with AP (+SAT), while if he or she is aiming for non-US including European and Singapore (everywhere else) universities, it is recommended to take IB.
Apart from that… It is hard to compare the difficulty because the nature of the curriculum is different. Hope this helps!

thank you so much!! Now I roughly get it... sorry one more, I see A level as well, is that a curriculum for UK?

NP :) Yes, if you are looking for UK / European universities, you can do either A level or IB. For A level you will need to choose the subjects (min three) so it is really subject specific, good if you know which studies roughly want to pursue at university. For IB it is more general, everyone needs to write essays and take 6 subjects etc.