that pad was done with the Future Retro XS and Eventide Eclipse.
the XS is patched pretty simply.
Osc1 set to saw wav, set 1 octave below osc2.
Osc2 set to saw wav, detuned slightly and hard sync'd to Osc1.
Osc1 modulates Osc2's frequency @ 25% intensity
Osc2 modulates Osc1's frequency @ 48% intensity
both Osc are mixed equally
Filter is set to low pass (2 pole) and set about 40% open
set amp env to taste
Filter Envelope stats out completely open and slowly decays to it's 40% open state
a triangle wav LFO modulates the filter as well and the filter is also being over
driven.
the FX on the Eclipse is one of the multiplex delay algorithyms.
i think people like FM for pads because they lend themselves to their production rather easily. being digital... chances are you'll have extra envelopes, LFO's, etc.
plus the nature of FM synths and their sets Operators which are made of a carrier and modulating pair.
so within a single Operator you have a sound... a sound modulator... your sound has an envelope.. the modulator has an envelope.... so you are able to bring in multiple timbres with multiple types and rates of modulation and different envelopes bringing in and taking out certain elements. Filter's aren't even needed when using FM.. BUT.. you can use a filter and one of my favorite things is to rythmically animate specific frequency bands in pads.