Panasonic ZS70 has a 20.0MP 1/2.3 (6.17 x 4.55 mm ) sized BSI-CMOS sensor and features Venus Engine processor. On the other hand, Nikon S5100 has a 12.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized CCD sensor and features Expeed C2 processor.
Panasonic ZS70's sensor provides 8MP more than Nikon S5100'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 ZS70 and S5100 sensor size comparison.
Panasonic ZS70 and Nikon S5100 have sensor sizes so they will provide same level of control over the depth of field when used with same focal length and aperture. On the other hand, since Nikon S5100 has 68% larger pixel area (2.34µm2 vs 1.39µm2) compared to Panasonic ZS70, it has larger pixel area to collect light hence potential to have less noise in low light / High ISO images.