WCF Advantages over Web Service
WCF supports more of the WS-* standards than Web Services. You can’t really do streaming or support atomic transactions etc in Web Services. WCF supports multiple binding’s HTTP, WSHTTP, TCP, MSMQ etc. ASP.NET Web Services has only http.
Web Services have no instance management, i.e. you cannot have a singleton web service, or a session-full web service. You can maintain state of web services but we all know how painful that is.
WCF while very similar to Web Services also incorporates many of the features of Remoting and .NET Enterprise Services (COM+ Services Components).
It is flexible and extensible like Remoting only more so.
It is compatible like Web Services only more so.
It is feature rich like Enterprise Services only more so
1) WCF can maintain transaction like COM+ Does
2) It can maintain state
3) It can control concurrency
4) It can be hosted on IIS, WAS, Self hosting, Windows services