Always use as much as possible Ground Plane!
If you have only GND Plane at the Bottom, and you forget to connect top layer assembled SMT components with their ground pad to the bottom layer, than you have a problem later...
Best is always using GND Planes on top and bottom, reduces EMI, reduces the problem described above and it is more easy to use SMT components like QFN components with heatsink/gnd pad in the middle. You only need to make some more extra gnd vias along the board outlines, thats important not to get later some dirty effects (More important in rf layouts). Keep attention not to get isolated areas also!
Regards,
Ralf