They are not comparable for "difficulty" as they are very different in terms in length, depth and age studied.
Personally I prefer the Scottish system where breadth is kept for longer and you can keep your options open if you change your mind what uni course you are going to do. Then you can go down to 3 AH in S6 if you want the depth and to be competitive for unis outside of Scotland.
Never had problems finding resources beyond the resources schools already provide/my own class notes for any of the subjects I took at NAT5 or Higher - HTP, Leckie, BrightRed, TeeJay, numerous websites, Scholar, youtube, SQA past papers, SQA understanding standards etc etc. How many resources do you have time to read during a 1 year course????