As Essencay says, it's unlikely that you'll find an dissenting opinion here.
WindowBlinds is good for skinners because it offers them the flexibility they desire because the engine is under the control of Stardock and they can make additions and modifications based on user feedback. A hacked uxtheme can never offer that, and so it's less skinner-friendly.
In addition, I would suggest that the performance of WB is going to be far in advance of that offered by uxtheme, if only because the XP one won't be changed one bit over the code available in 2001 while WB has had over three years of futher tweaking to reduce memory footprint and CPU usage.
So basically my argument is that WB can do more, with less, and it has a history of good support. What more do you want? (the suggestion box is always open

)