I suppose it depends on what you are good at. For example, I am rubbish at English so i find that the hardest.
As for what each course entails, to my knowledge, Maths, Bio, Chem, 3 units and 3 NABS fairly simple to Understand.As for English There are 3 parts that make up your final grade: Close Reading, Critical Essays and a folio.Internally: you need to do a Close Reading and textual ANaylsis NAB.Finally, for German( I did French and teh formats the same)/ Internally , you need to pass Speaking, Reading, Listening and ERV. Where as the final exam is made up of these parts. BEWARE, Listening is the hardest part of teh exam , it is the only part of the exam , that you would be proud of getting half of the marks.
Another word of warning, For your BIo and Chem courses, SQA are implementing new Higher science courses from 2012, so there will be no study books and Past papers that are the same as the ones you are going to sit. But they may publish something over teh summer.
A final thing , Maths, i am good at maths but when it cometo the exam it is murder. I passed the uNit 1 NAb(100%) coping easily with the coursework and finding the homework relatively easy for the full year. BOOM, come Febuary, the prelim, the whole year was nearly reduced to tears after coming out of teh prelim.Most difficult exam ever. The point is that for ALL your subjects, DONT BE LED INTO A FALSE SENSE OF SECURITY BECAUSE YOU ARE BREEZING THROUGH YOU'RE NABS AND COURSEWORK, the final exams are a different kettle of fish.
Anyway, Good Luck and best of all enjoy it ( though i can hardly say that, i am in 5th year and at times , i want to kill myself, 5 highers, not easy!)