I think Nidorino/Nidoking's only good level up moves are double kick (NidoranF, level 12), thrash (Nidoking, level 22), and megahorn (Nidoking, level 43). Poison sting and fury attack are weak, helping hand fails in single battles, and flatter and horn drill are unreliable gimmick moves. Horn attack is decently strong, but there's no reason to use it when you can learn thrash just as easily.
The later you evolve Nidoking, the longer you have to use a weaker Nidorino. So I recommend evolving Nidoking as soon as you have a double kick Nidorino and a moon stone.
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