Selecting between openfire or ejabberd

hi all

I am new to char server and currently we have chat server setup on openfire . now we are considering to migrate to ejabberd as we will have large number of concurrent users for our app . So I want to know whether it is good decision to migrate to ejabberd . How many concurrent user openfire can handle and is it easy to modify as ejabberd is written in erlang . which one is more good at production