Between a full wave rectifier circuit and a half wave rectifier circuit which has a better(i.e lesser) voltage regulation?
Average output voltage for a 50Hz mains and half wave rectification is approximately:

\$\sqrt{2} V_{RMS} - V_F - \frac{20ms\cdot I_{OUT}}{2 C}\$ where VF(I) is the forward voltage of the rectifier, and C is the filter capacitor value

For full wave rectification it is : 

\$\sqrt{2} V_{RMS} - 2V_F - \frac{10ms\cdot I_{OUT}}{2C}\$

So for a given filter capacitor, the output will change twice as much with current change. That ignores the rectifier forward voltage change with current. If the filter capacitor is doubled for the full wave (to maintain the same ripple voltage) then the full wave will have worse regulation because there are two diode drops in there and each increases with increasing current.