@Named gives a CDI managed bean an EL name to be used in view technologies like JSF or JSP. Note that in a CDI application you don't need the @Named annotation to make a bean managed by CDI (thanks to @Karl for his comment).
@ManagedBean makes the bean managed by JSF and you can:
- inject it into other @ManagedBean annotated beans (but not into @Named beans!)
- access it from your views via expression language
See this related question for further information how injection works among both kind of beans.
Note that there is also a difference with the scope of the beans. They come from different packages but are named identically (JSF: javax.faces.bean, CDI: javax.enterprise.context , so it is often a source of error and confusion if you include the wrong class.
From my experience: You should use CDI beans whenever possible since they are more flexible than JSF managed beans. Only drawback is that CDI doesn't know a view scope, so you either need to fall back to @ManagedBean or use some third party extension like Seam.
