Web application programming interface which is primarily used for the creation of full-blown REST a service which implies that WEB API does not NEED any data configuration and contracts to the level of WCF.
WCF was created for the development of SOAP-based services. It uses STANDARD XML and schema over HTTL which leads to the degradation in the performance of the application.
WEB API support Any media content format
It uses Text format that includes XML
It uses URL patterns, HTTP methods as a service interface
WCF uses service contract as a service interface
The caching mechanism of WEB API is built-in HTTP application control
The caching mechanism of WCF service is handled by the application