WCF:

1. We can use Http,Tcpip,msmq protocol.
2. It is recommended when we need transaction or need to develop chat services etc.
3. WCF need lot of configuration.

Web API:

1. It uses only Http protocol.
2. It is recommended when service to be consumed on web,mobile or on low bandwidth devices.
3. We don’t need too much configuration like WCF.