Six analytical expressions (four of which have been published recently) for the equation of state of a hard sphere system, together with two different expressions for the molecular diameter, have been tested in order to reproduce molecular dynamics results for pressure and potential energy of the Weeks-Chandler-Andersen reference system for the Lennard-Jones potential. The best choices for the combination of equations of state and molecular diameters in the calculation of those properties are given. It is shown how that choice may differ for different ranges of temperatures and densities, and how there is not a direct relation between the simplicity or complexity of the analytical expressions and their accuracy.