chem - conquering or contexts
maths - fitzy or cambridge
and btw. from my POV fitzpatrick is better. even though the layout of the book is boring and it doesn't have A LOT of questions, they are very good~
cambridge is alright. i use both. we get given cambridge and i have fitzpat for further reference.
and yes cambridge is challenging .. for most students if not all. however i personally feel unsatisfied because i have to 'select' questions to do instead of doing every question (which will take for than 3-4 hours miniumum, TRUST ME!!!). i only do the work because it's set by the teacher. (who usually checks if we've been good or not)
it's a personal thing. but i love fitzpatrick!!!!!
and that's my two cents