Which user acceptance testing metrics is more effective for business?

One metric I find very telling is how many defects are being found per day or week. You might think of this as the defect discovery velocity. These must be analyzed in terms of severity. So, 10 new minor defects may be more acceptable than 1 critical defect. As the deadline nears, the number of new, critical, defects gains even more importance.

Another important metric is the number of resolved/unresolved defects. These must also be balanced by severity and should be reflected in the acceptance criteria. Be aware, though, that it is common (and not good) practice to reclassify critical defects as "moderate" to release the system on time. Also, keep in mind that you can "die the death of a thousand paper cuts." In other words, it's possible to have no critical issues, but many small issues that render the application useless.

Acceptance criteria coverage is another key metric to identify which criterion have and have not been tested. Of course, proceed with great care on this metric as well. Just because a criterion has been tested doesn't mean it was tested well, or even passed the test.

Finally, stakeholder acceptance is the ultimate metric. How many of the original acceptance criteria have been formally accepted vs. not accepted. It may be the case where just one key issue holds up the entire project.

I would point out two metrics which is effective on Business.  Number of Defects found and the stakeholder acceptance.

The earlier one may be considered with the Criticality of the Defect found. The later one to be considered by the number of defects accepted and not accepted. Accepted and not accepted again triggers the question of the criteria on which the acceptance happens. whether it is based on the criticality /  based on the release.

However, the whatever the metics used in the business process, the consideration should be focused on Value of the UAT and the quality of the System released.