They are both useful. They configure two separate communication channels that are used by different clustered services. The tc5-cluster.sar one is used for HttpSession replication. The cluster-service.xml one is used for most everything else (except EJB3 which has its own channels if you use it.)
Thank you for your reply!
On your opinion, If I only want to implement the Session replication, I only need to configure the tc5-cluster.sar?