Imo Adamant Nature is the best Nature for each of the Pokémon you have mentioned above. Adamant Nature increases the Attack Stat and decreases the Special Attack Stat.
Although if your running Endeavour on Aron give it a Timid Nature, if your running a Defensive Lairon give it a Careful or Impish Nature, and if your running Rock Polish on Rhyhorn, Rhydon or Rhyperior give it a Jolly Nature.
Hope I helped :)
