Comparing these two approaches, I would rate your overall performance between them. Assuming you have the ability to pursue either / or, I found that the logistics work with Metro and AXIS2 would be higher than WCF.
Given that both of these are access points, any system complexity lies behind the scenes in terms of compatibility — these are key decision points. Although we live in a world of unlimited interoperability, I prefer stacks where consistency can provide performance and productivity.
Regarding open-source, while on the Java side more than on .Net, I also found that more of these projects are built to support functionality not available in the Java web services platform (RESTlet, for example.)
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