I've got a 100% Nidoking with his best moveset and I don't think that is really worth it for me to power up at this time. Just saving it as a trophy.
Megahorn is the strongest bug type move, but he doesn't get STAB and the main pokemon that you would want to use bug moves against is Exeggutor, which will rip through the poison type Nidoking with its strong psychic fast moves. Parasect, Scyther, and Pinsir are all better bug choices.