The most stable resonating structure is the one with no charge separation. This corresponds to \(\mathrm{P}\).
This is followed by Q as it has an octet of all atoms complete. None of them is electron deficient.
The resonating structure with a positive charge on a relatively electropositive atom and negative charge on the electronegative atom is more stable than the reverse case.
Order of stability is:-
\(\mathrm{P} > \mathrm{Q} > \mathrm{R} > \mathrm{S}\)