I have worked only with Trinidad and Richfaces. I like both but I would give the edge to Trinidad. It may be because I have worked with it more and I feel more comfortable with it. Trinidad online documentation is also good enough.
Both Trinidad and RF have a lenghty component library. You can check those links to see what components you will find useful to your application. I have used Trinidad tree in one recent application I developed and it was easy to use and fill: Trinidad components - RichFaces components (login required)
Regarding skinning I feel Trinidad default skinning to be more basic than RichFaces one but I think both have ways to make them as beautiful as your CSS skills allow you.
I think RichFaces has a more mature AJAX integration and their AJAX components and events are more easy to use for me than Trinidad ones.