When building a WCF service for a large scale application, which is better:
In both cases, assume that the business logic layer is separated into a different assembly.
Using your business logic layer as a service implementation i.e. with no code behind and no wrapper
<%@ ServiceHost Language="CS" Service="MyApp.BusinessLogic.BusLogicImpl" %>
or
Using the codebehind of the WCF service that wraps calls into your business logic layer.
<%@ ServiceHost Language="CS" Service="MyApp.WebServiceHost.Service" CodeBehind="Service.svc.cs" %>