I crashed higher modern studies this year, but I can't give much information on English personally.
I think it all depends on what you are looking to do once you leave school. If you are going to apply to university in Scotland then advanced highers usually aren't required for first year entry. The workload for advanced highers is considerably more and considering that you're doing art and music then they will require a lot of time too. A lot of people in my year got to prelims and dropped advanced highers due to the workload and the fact that they got unconditionals.
I personally find modern studies really interesting and I'm predicted an A this year. The essay writing skills are very similar to higher history. The workload for me has been quite minimal and usually consists of writing essays or completing source questions. It's useful if you keep up to date with current affairs as you can use your own research in your essays. The topics are interesting (depending on what your school do) and we're doing democracy, social issues and terrorism.
However, if you enjoy English more then perhaps consider taking it, because if you enjoy a subject then doing the work isn't as bad haha.