There is no "best" project. It depends on you. The whole purpose of a project is for you to learn something, and something that you want to learn. Think about your interests and what you have studied in the past and would like to know more about. Use the internet to find out more and think about what would make an interesting study to share.
I think a volcano...
but not just any ordinary volcano one with rainbow sparkles.
You could make it bigger than what its supposed to look like.
Here are some volcano videos you could watch:
(but you can add sparkles)