heat map objective function?

I generate several Z heat maps (X,Y, Z=performance) by varying the X and Y functions. I want to pick the best X,Y functions based on the heat maps.

A heat map with a smoother surface is better than a rough one. Also, one that separates high performance from low performance is paramount.

Any ideas on how to algorithmicly use these two(or more) criteria to pick the "best" heat map?

heat map objective function?