Casio EX-S5 has a
9.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized CCD sensor . On the other hand, Casio EX-ZS5 has a
14.0MP 1/2.3-inch (6.16 x 4.62 mm ) sized CCD sensor and features Exilim Engine 5.0 processor.
Casio EX-ZS5's sensor provides 5MP more than Casio EX-S5's sensor, which gives a significant advantage in real life. You can print your images larger or crop more freely.
On the other hand, please keep in mind that Max sensor resolution is not the only determinant of resolving power. Factors such as the optical elements, low pass filter, pixel size and sensor technology also affects the final resolution of the captured image.
Below you can see the EX-S5 and EX-ZS5 sensor size comparison.
Casio EX-S5 and Casio EX-ZS5 have almost the same sensor size, so neither of them has any significant advantage over the other in terms of providing control over depth of field when used with the same focal length and aperture.