Lets not confuse the SW9 with the SW99. The SW9 is the new sigma and from what I understand is a huge improvement over the old sigma.

The SW99 is a Walther P99 built by Walther for Smith and Wesson. In the pic below you can see the Walther name right behind the accessory rail.



This is the SW9


This is the SW99



To answer your original question my pick would definetly be the XD over the SW9.