Which testing type primarily focuses on the system's behavior and experience from a user perspective?

User acceptance testing (UAT) primarily focuses on evaluating the system's behavior and experience from the user's perspective because it is conducted by the end-users or clients to ensure that the system meets their requirements and is ready for deployment. During UAT, users validate that the system functions as intended in real-world scenarios, confirming usability, functionality, and overall satisfaction. This hands-on involvement allows users to assess how well the application meets their needs and whether it is intuitive and user-friendly.

In contrast, unit testing, integration testing, and regression testing have different focuses. Unit testing is concerned with examining individual components for correctness, primarily from a developer's perspective. Integration testing assesses the interactions between integrated components, ensuring they work together as expected rather than focusing on user experiences. Regression testing, on the other hand, checks for new defects in existing functionality after changes have been made, concentrating on the internal workings of the system rather than how users interact with it.

Thus, user acceptance testing stands out as the testing type that emphasizes user experience and behavior, making it the correct answer for this question.