What question should I pick for my EPQ?

Factors to consider when picking an EPQ question
Where do you want to go with this EPQ? If you want to include it on your personal statement for university or even talk about it during a university interview, it's important that it links to your chosen degree subject.
What area of your chosen subject should you focus on? It might be useful to explore some of the most dynamic current issues in your chosen subject - read a journal or magazine to see what academics in the field are interested in at the moment. This will be more interesting to someone marking than picking a question which has been discussed for centuries, and will be particularly useful if you intend to show initiative and curiosity in a personal statement or interview.
Are there enough research resources in that area? While picking a more original subject area will help you to score highly in an EPQ, it is essential that your answer is thoroughly researched - check that you know where you will get your evidence/sources from before you decide on a niche question
What do you genuinely want to know? Passion for the question you've picked is very important: not only will you have to write extensively on it and research it for months, but you have to have an opinion. It's not enough to just examine an area of academic interest, the best answers will make thoughtful observations and conclusions about the research they have encountered.