Hi, I am doing a web service testing on a ASP.NET web site
and I am confused about InstanceContextMode of ServiceBehavior
Basically there are three instanceContext modes in WCF

Per-Session instance mode
Per-Call instance mode
Singleton Instance Mode

When I look at the code for wcf service code for the three servcies, in the production environment, I see that

[ServiceBehavior(InstanceContextMode = InstanceContextMode.Single, ConcurrencyMode = ConcurrencyMode.Multiple)]

What I want to ask, per-call and per-sessions are more fast ?
But the underlying web site uses basket system (it is (a shopping chart system)
So, does is have to be single mode ??