I did Computing, Physics, Maths and Biology. They honestly all had equally hard modules, in Computing I found the theory side difficult to pin down - the inner workings of a processor, RAM, ROM etc. I found it hard to memorize it all. The same thing happened with Biology, the shear amount of stuff you have to remember is just insane.
Maths and Physics wasn't that bad, it was just about applying what you learned to different situations and scenarios.