Demanding in difficulty, or demanding in job prospects at the end?
All degrees are going to be difficult, especially at the top universities. STEM subjects are notoriously difficult, but you have a lot of contact hours and good lecture slides which will help. Essay subjects will require a lot of reading and independent work outside of contact hours, so you have to be motivated to work outside of class. Dissertations are difficult, and they will come up no matter what you do.
As for jobs, there is obviously a push for STEM subjects at the moment more than anything, but there is plenty you can apply to any degree.
If you are sure that university is for you at all, consider the subjects you like at school, or the topics you find interesting. Think about career options for you and look at degree courses or college courses for them. Make sure you choose something you're interested in, and then the workload will be a little more manageable because you'll actually want to do it.