I'm about to create an API for a existing .NET application and want to go the RESTful service route. Our backend platform is .NET and MSSQL. I'm hoping for a good blend or scalability combined with clean architecture. 

Are there any strong opinions on the best way to implement a RESTful .NET API (WCF, standard ASP.NET, MVC or even HTTP Listener)?

Also any opinions on why NOT to go with .NET or reasons to use something like RoR.

Thanks in advance for any opinions on this topic.