Suggestion to choose correct WCF Instance Mode & Concurrency Mode

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WCF

serialization

I am Balu from Hyderabad. I have writing WCF Restful services for our Andriod / Iphone developers. They can use JSON format so that we are choosing REST. Actually we can do Mobile Application only one APP that can runs differnt projects. All the projects are dynamically comes from WEBSERVICE to MobileApp. So we can configure all the dynamic data from Web services only.

Only one App can handle 5 projects having totally 100-150 users. so i can write only one service using Factory Reflection methods to load projects dynamically.

Q) I have doubt that for our projects which WCF instance mode is suitable?
By reading WCF instance mode articles i understand that "percall" instance is suitable for our WCF service. Is my guess correctly or not? Please suggest me.
And I have one more doubt that if we are not specify an attribute as serialize then that object will not go through network properly? I have tried without serialization (i.e. not mentioned "datamember" for particular property) its going well to Mobile App.
Please clarify my doubts and tell me which instance mode I have to use?

1. Which instance is better?
2. Which ConcurrencyMode is better?