Which type of UML diagram is best for modeling workflows?

The best type of UML diagram for modeling workflows is the Activity Diagram. This diagram is specifically designed to represent the flow of control or data within a system. It visually outlines the sequence of actions and decisions, making it particularly effective for illustrating how various tasks and processes are executed in a workflow.

Activity Diagrams depict activities and their transitions, providing a clear view of parallel processes, decision points, and the overall flow of control. This allows for better understanding and analysis of workflows, making them a valuable tool for both developers and stakeholders when identifying processes that need optimization or clarification.

In contrast, Class Diagrams focus on the structure and relationships of classes in a system, Use Case Diagrams illustrate interactions between users and systems rather than workflows, and Collaboration Diagrams emphasize object interactions rather than the sequential flow of activities. Thus, while all these diagrams serve specific purposes, the Activity Diagram is uniquely suited for detailing workflows effectively.