Do you lean more towards testing the user interface or the application's API layers?

The choice between testing the user interface (UI) and API layers depends on the project's goals and context.

UI Testing checks how the end user interacts with the application, including visual elements, navigation, and interface behavior. It is important for assessing usability and correct display.

API Testing focuses on verifying business logic and interaction between components through application programming interfaces. It is usually faster, more stable, and easier to automate because it does not depend on visual changes.

It is often recommended to start with API testing to ensure the correctness of the basic logic, and then cover critical user scenarios with UI tests. This approach provides a balance between speed and thoroughness of testing.