Zopim seems quite nice and user-friendly at first look. However this is associated with a pretty high price...and its per agent? Come on, who charges like that?! Even if I have a small company with 5 sales agents, it still is too much
Ourselves, we use a very redesigned version of PHPLive! Support, tweaked to serve our needs. In my eyes a good chat software shouldn`t be too complex with hundreds of features. What you need are basic capabilities like "typing" indicator, transfer chat ability, canned responses option, customer information fields and just a few more. Everything else is just personal preference without any significant benefit to the chat process itself. I personally like the rating/comment option at the end of chats, because they provide valuable information to the host and shows where certain agents need to work upon.
Whichever software you choose, avoid keeping its basic outlook - modify it, make it look different, make it look like YOU! Its just another of the many faces of the company and you don't want to have a chat console the clients have seen numerous times before, used by other competitors they have checked. Be personal, be unique