WCF RIA Services vs WCF Services ?
First, Here is a great article from Shawn Wildermuth where he pointed out the pros and cons: Choosing a Data Access Layer for Silverlight 3
Second: Arturo Molina said:
"Actually, you can use the same validation and auth without using RIA Services. What RIA Services gives you is code generation. It creates your classes for you. You only need to put the business logic. I think RIA Services is very useful for developing small to mid apps very rapidly.
Another difference is that it hides the asynchronous calls to the web service. Many people don't like the async model (which is the only one you can use in Silverlight) and RIA services handles that for you.
I recomend reading this article from Shawn Wildermuth where he points out the pros and cons from both approaches and also includes ADO.NET data services (which is now calles WCF Data Services, I think):"
Third: Martin Liversage said:
".NET RIA Services was created for Silverlight that runs in the browser. Silverlight is running a special version of the the .NET framework and in an N-tier application Silverlight is unable to share assemblies with the server side. By employing some clever code generation .NET RIA Services makes this gap almost invisible to the developer. Classes similar to the domain classes are code generated on the client side, and ways to move objects back and forth between client and server are also made available.
You will probably be able to call into a .NET RIA Service from Windows Mobile, but I don't think it will particular easy and currently you may in fact have to reverse engineer what's sent on the wire (JSON is used). WCF on the other has a much more broad scope, but doesn't support Silverlight development in the same way that .NET RIA Services does.
If you are writing a Silverlight only N-tier application .NET RIA Services are very powerful. If however Silverlight is only one of several clients WCF is probably a better choice."