Web service:
The File extension of web service is .asmx.
It can be hosted in IIS.
[WebService] attribute has to be added to the class.
[WebMethod] attribute represents the method exposed to client.
One-way, Request- Response are the different operations supported in web service.
System.Xml.serialization name space is used for serialization.
XML 1.0, MTOM(Message Transmission Optimization Mechanism), DIME, Custom.
Hash Table cannot be serialized.
Only public properties/fields can be serialized.
Unhandled Exceptions returns to the client as SOAP faults.
Slower than WCF.
Uses only SOAP(Simple Object Access Protocol).

WCF:
The file extension of WCF service is .svc.
It can be hosted in IIS, windows activation service, Self-hosting, Windows service.
[ServiceContraact] attribute has to be added to the class.
[OperationContract] attribute represents the method exposed to client.
One-Way, Request-Response, Duplex are different type of operations supported in WCF.
System.Runtime.Serialization namespace is used for serialization.
XML 1.0, MTOM, Binary, Custom.
The DataContractSerializer translate the Hash table into the XML.
Public/Private properties/fields can be serialized.
Better than WebService. The performance measures in terms of xml serialization.
It can send/receive message in any transport protocol message format. By default it uses SOAP for communication.