WCF-NetMsmq vs MSMQ adapter

The upcoming BizTalk Server R2 extends heavily the messaging capabilities of BizTalk Server. Together with the rich messaging engine the WCF adapters and the WCF Line of Business Adapters SDK opens a whole new set of possibilities for developers. However, there is still some overlapping between the messaging features of BizTalk and WCF that developers must understand in order to apply the correct technology to a particular scenario. One of the most interesting scenarios with these characteristics is the interaction with MSMQ for achieving asynchronous and persistent messaging. Since the 2004 release BizTalk Server includes a MSMQ adapter for addressing this type of interaction. Now, with the WCF adapters included in R2 it is possible to use the WCF-NetMsmq and the WCF-Custom adapters for achieving similar scenarios. The question then becomes when to use one option versus the other.