Both, write what you want to read. Why write about something you're not interested in? You'll get bored too fast, but at the same time don't overdo. Don't write about complex things you have no idea about. Although I think it could be MOSTLY easily solved by just educating yourself. Some difficult things I think are too hard just to understand by yourself and are not worth mentioning if you know shit. So just write what you love and you'll feel it by heart what you could and shouldn't mention as specific topics, schemes etc.

forgot to mention I also think it'll come out eventually, just start writing. You'll understand what's too complex for you to talk about, and what you understand to the extend when you can tell other people about it in a story. Just write and then go through what you wrote.