see i think c3 is easier, buts its harder beacuse its easier, the first 5 chapters you will find easy and fly through them and the last 3 are the hardest with trig in my opioion the most difficult !!! c2 is easy once you understand it but because its quite a range of topics its takes more time.
but you have to do them anyway to get an A level maths so you cant really avoid them but in my opinion do c2 first and then c3