The silicone eartips are a bit smaller and softer than the foam eartips. They will provide a comfortable feeling in the ears like they're not even there.
The foam eartips are made from memory foam so you'll have to warm them up in your hands before putting it in your ear. That way, they will take the form of your ear canal and provide a better experience, but they're less comfortable. Feel free to try them both out and you'll find out very fast which you prefer!