Whatever capacitors you do use, it has to be non-polarized, and ceramic dielectric or better, and have a voltage rating far beyond your circuit operating voltages (probably 100V for your 24V circuit). Since your snubber is not a very "serious" snubber, you can probably get away with using ceramic capacitors.
SIzing is kind of a black art...see PDFs. In summary, a large capacitor will snub better, but will require a higher power resistor to dissipate the energy. Yours is a relay application so it's not really high speed like most circuits that need snubbers so power dissipation is probably not a very big problem for you (and that's where most of the tradeoff for snubbers comes in aside from cost). Just try regular values...0.1uF x7R 100V capacitor with a 1 carbon composition ohm resistor.
Inductive spikes usually harm the switch trying to disconnect the current and for relay. For a relay, this usually means the switch driving the relay coil, not the primary contact since it is basically a piece of wire...not much inductance there. I don't see how sparking across the relay contacts would damage the LED though. The voltage spike appears across the switch, not anywhere else. THe parts are cheap and common though so it's worth a try.