It depends, but always use user and password for normal case, key authentication is not recommended until when you are trying to configure some cluster environments by using (corosync & pacemaker or heartbeat & pacemaker) and drbd (Distributed Replicated Block Device) and some other services which requires key authentication (not ssh key auth).
Up to my view Yes you can login into multiple servers by using ssh, pssh but here you can only retrieve the info from those hosts and you can save it in your local machine.