Hi Louis,
the PWM keeps the same frequency of the waveform and changes the duty cycle, to change the power transferred, while the PFM modulation keeps the same duty cycle and changes the frequency to change the transferred power.
In skip mode some of the pulses are skipped to lower the power transferred.
Regarding the EMC, the skip mode is the worse for the EMC to other devices. For the PWM and PFM, its not that easy to answer. It depends on many aspects. Please check a quote below.
With Best Regards,
Jozef
