I've used ESO at two places and it is far superior to my only comparison which is zoll. One my supervisors is a consultant for them which helps too.
I've heard good stuff about it. No idea why we didn't choose them.
I've used Zoll and it was just ok. We did have an issue of the servers losing reports during and after syncing.
A good friends significant other works for ESO. No idea what he does though.