Lasers are, in theory, more effective.

Lasers discharge a single wavelength which targets and destroys the hair follicles. However, not all lasers are the same. The laser needs to be long-pulsed and should emit one of several wavelengths. I personally use the long-pulsed 1064nm Nd-Yag laser for my hair removal treatments.

IPLs emit multiple wavelengths, some of which are absorbed by the skin and other structures. This limits the energy used as we want to prevent burning the skin. Good IPL machines should filter off the unwanted wavelengths thus allowing higher energy levels to be applied.