My votes go to open source WCF. Like many of the .Net libraries WCF classes become sealed exactly where I want to change their behavior. This is especially true for all things security. Sometimes it is really important to tweak the way WCF signs a message or handles a signed one but today this requires to implement a very long chain of extensions.
The current predominant features also include support for REST in the routing service and web sockets support on earlier windows versions. So far the traditional request to simplify configuration and bindings is not too visible, possibly because the WCF simplification features have done a great deal here (or because people are more focused on Rest these days).