Explanation
According to the PMBOK Guide, 7th edition, one of the key principles for project delivery is to "focus on value" (p. 10). This principle implies that the project manager should measure the project performance based on the value delivered to the customer and the stakeholders, rather than the output produced or the effort expended. The team that completes the most stories selected from the sprint backlog is performing better, as this indicates that they are delivering the highest priority and most valuable features to the customer. Story points are a relative measure of complexity or size of a user story, and they are not comparable across different teams or projects. The team with the least amount of defects or the team with fewer story points are not necessarily performing better, as they may be delivering low-value or low-quality features, or working on easier or smaller stories. References: PMBOK Guide, 7th edition, p. 10; PMP Exam Content Outline, Domain I: People, Task 2.