I've just started with AS. My opinion would be, like xplodedtb said, A-Levels is more of studying and the base of the syllabus in similar to IGCSE. However here things are taught more in depth and if you're career oriented and you could mange the studies, you might as well take it.
In IB, according to me, you would be spending more time on CAS etc. than on studies. I don't know what timings your school offers but at mine its usually 8.30-4. Some students reach home at 5 or 5.30 and find it difficult to manage their time- They've got their homework, coursework, revisions, tuitions etc. and tend to sleep very late. Also they get free time in school, according to their subject choice, and loiter around the school and do nothing productive as such. Well, obviously it depends on you but I just thought of mentioning it. This might affect your studies and if you ask me, IG is the easiest definitely, then A - Levels and then IB. Plus you've got 6 subjects in IB, so if you can manage that as well, well and good.
If you see, our school does have extra-curricular activities. So if you ask me, we wont be that bored only studying
Whatever the curriculum, it totally depends on how good the school is.
