ASP.NET Web API has many advantages but main of them are

• It works the HTTP way using standard HTTP verbs like GET, POST, PUT, DELETE, etc. for all CRUD operations
• It has Complete support for routing
• In .net Web API Response generated in JSON or XML format using MediaTypeFormatter
• has the ability to be hosted in IIS as well as self-host outside of IIS
• Supports Model binding and Validation
• Support for OData