they deal with interference in different ways, PPM (FM) processes TX signal even while interference is causing undesirable output from the RX. PCM will go into fail safe and 'Hold' the servos blocking out the interference and the TX (you have no control at all what so ever for a set amount of time)

PCM in my experience (as always YMMV) is far superior to blocking out interference that would cause less then desirable results in a PPM RX. i fly PCM only in all my high $$$ plans/jets and all seven of my helis, i even use PCM for cars because of it's fail safe features.

the servos are one and the same for PPM or PCM, there are however a few that will not work with a PPM receiver, the JR 8700G being one which I've got several of, they'll only work with a PCM RX

kc