There is no “ultimate” billing solution, as there is no ultimate medication good for all patients against any sickness.
Check that it has the features which are the most important _for you_.
For example one of our clients was really annoyed by the fact that he was unable to specify in VoiceMaster rate change in advance, plus he had compatibility problems between his Sysmaster and his partner’s Ciscos – these were few of the reasons why he stopped using it.