All of them modifies the base Templates of WPF Controls. Regardless of their "beauty", I'd choose one that is easy to Customize, maintain and documentation.
I personally never used one, but Modern UI is quite famous, sort of maintainable, have a lot of resources if you search and their site provides some tutorials on how to customize. If you haven't a lot of experience in WPF Templates, Styling, all of them will be hard to digest.
If that's not your case, choose the customizable one - whichever it is.
By customizable I mean not only the appearance, but the whole WPF purpose, architecture and patterns.