The Dense's Planet

In our solar system, we had a huge planet Jupiter start to form and it must have started from a gravitational over density. The bigger it is, the faster it's able to gather mass and the bigger the planet ends up being. And voila, that's how we got the planets. Some of them are denser than others and some of them is going to win the title of Dense's Planet. I guess another one is going to winning the Fluffiest Planet, which is the one where I want to go.