Vest thing to do is choose the one you can write the most about. Over the summer I would recommend you find a topic that has 5 to 8 subheadings. Make note of useful or used websites and create a progress log on what you've done and how it went as well as targets. Use the subheading to divide down the word count to ensure it is realistic.
If you have time as I know its summer, I would gather a range of information such as video, documentaries, books as well as think what you can do for primary data.
I will worn you 16 people in my year applied for the EPQ and by January there was only 4 of us as many people hadn't kept up with the work due to ucas applications. Getting a head start helps prevent this and gives you a better chance of seeing it through. That being said the support in my school wasn't great.