Depends on what you are looking for in terms of features. If you want to build a global cluster, give ejabberd or its forks a shot. I was running it in the past

Depends on what you are looking for in terms of features. If you want to build a global cluster, give ejabberd or its forks a shot. I was running it in the past and it was just running without any problems. I picked it because of its clustering features and ldap support.