I am using JSF 2.0 and I am looking for a copmponent library with minimal load in terms of performance. Which one is better to use if I have choice between RichFaces and PrimeFaces? What are the advantages and disadvantages of both?
Richfaces is definitely more mature and possibly you may get developers who are experts in.
Primefaces has more components but lack combobox available in Richfaces. Richfaces does not have a bunch of common components like the "star rating" component, captcha component and password strength.
Primefaces is easier to skin since it is based on themeroller. It also has more themes than that is available in Richfaces.
Primefaces is tiny and can be implemented in the code easily - not too many dependencies.
Richfaces does not support JSF 2.0 till now (Nov 2010) - Primefaces has a stable release that supports JSF 2.0
Richfaces component growth is pretty much absent... No new components added in the last few years. The component library remains stale.
My recommendation:
Choose Primefaces if your application is client facing and need many AJAX components.
Choose Richfaces (or Primefaces) if it is an application that is used by your internal clients.