I think I like the CSS Hat model better because it generates the code that I then have complete control over. First, that can be helpful when learning the language. Second, it's really nice because of its tweakability. If the CSS Hat dev's decided to implement a stroke as a border, but I know it would look better as a layered drop shadow, then I can make that adjustment. If there are any other quirks or bugs, I can fix them with the resultant code. With the pixate model, I can't do that, as far as I understand (please correct me if I'm wrong!!).
You can edit the CSS with Pixate in the exact same way. It doesn't get 'compiled away', the runtime optimizations happen behind the scenes. The CSS can remain in your project as a resource, much in the same way you reference your CSS in an HTML page.
