I'd like to propose a new winning criterion: Parallelize as much as possible. A challenge of this type is to give a code that involves parallelization.
Let \$T\$ be the running time when run on a single processor. Due to Amdahl's law, as there are more and more processors to be run on, the overall running time will converge to a positive value \$t\$. The submission whose the ratio \$t/T\$ is the smallest shall win.
What are the caveats?