This week's giveaway is in the EJB and other Java EE Technologies forum. We're giving away four copies of EJB 3 in Action and have Debu Panda, Reza Rahman, Ryan Cuprak, and Michael Remijan on-line! See this thread for details.
I would stick with http://repository.jboss.org/nexus/content/groups/public/ because that's what I am aware of as the public repository. My guess about the first repository is that it contains only JBoss specific Maven artifacts and probably doesn't have 3rd party maven artifacts. I'll check with Paul Gier who manages the JBoss Maven community repos.