Personally I would take the XR5 over the 3MPS. THe focus has a bit more pedigree (i.e. the
WRC), and I think it generally is more appealing to the eye.
The Mazda 3 MPS is a 2.3 vs the XR5 being a 2.5. However the MPS is quoted as making 190kw/380nm and the Focus only 166kw/320nm with the wieght of each being almost exactly the same (1408 vs 1403). The new shape MPS hasnt been released yet though and that gets a 2.5. Having said all this as phizzle has said in above post there are a few options for the XR5 to get a bit more oomph.
Even with the differences in output, I personally would still have the Focus...
Compare them here...
Mazda 3MPS Sports
Ford Focus XR5