Adamant is pretty good. Sp.Atk isn't needed and I think you'll notice that the added power really helps Earthquake. Steel and poison types aren't going to get poisoned, but both are weak to Ground. That extra power can really help out in the long run. Losing some defensive stats by not having Careful or Impish isn't ideal, but good EV training can make up for those shortcomings.
Hope I helped!