We recently are trying out
* Potential CPH-Does not include idle time
* Success/Hour
Then you may use some metrics specific to your industry/campaigns such as $/hour or errors/call (from QA).
We are developing another metric to capture the long-term effect of the call on retention campaigns. For example, if the agent waives the customer's account, this is counted as a success, but the customer may become delinquency again. The new metric counts actual revenue/expected revenue, and it's prorated over time.