Rhydon optimal moveset?

Stone edge has a higher DPS but for a shorter duration so if you do a weighted avaerage to quick and charge move DPS Earthquake has a greater effect on overall DPS.

I also find monotype attack slightly more useful

I've got both (with mud slap) and find that in real life there's little to choose between them.

Use these sites for reference, but trust your own battle experience. I've used an IV 73, 2100 CP Rhydon with mud slap and stone edge against 2400+ Snorlaxes and won easily (no dodging quick attacks, only the special attacks). So I know for sure I've found a solid option vs Snorlax, which tormented me before.

Stone edge is better against Ice, flying, bug and weaker to fighting and ground.

EQ is better against electric poison and rock and weaker to Ice.

Against Fire they are about the same, the one you like is prolly better and both are weak to grass and water. I think EQ is prolly better rated partly because of the typing/resistances more than damage.