It seems to me that it comes down to battle between Prism and FreshMVVM - this brings me to my most important questions:
No Xamarin Forms does not offer navigation like Prism. They had a goal of making the built in Navigation similar to Prism, but that has since disappeared from their roadmap. There is also no direct IoC concept built directly into Xamarin Forms.
If you are developing native UI's then Prism probably isn't for you as it is purpose built for Xamarin Forms. In that case I might say you should look at MvvmCross. It is battle tested in a lot of classic Xamarin apps.
If however you are developing with Xamarin Forms, then Prism would be the best to use. My opinion may be biased, but it's also the public opinion of many of those on the Xamarin team. Remember Prism was originally started by the Microsoft Patterns and Practices team. While Prism for Xamarin Forms was started after that, the foundation of what Prism is and how it works, helps keep developers developing using proper MVVM patterns.