Here's what I think...
Ability: Sheer force
Nature: Adamant/Jolly OR Timid/Modest
Adamant/Jolly set: Earthquake (STAB), Poison Jab (STAB and boost from Sheer Force), Shadow claw (covers Psychos+Sheer force boost), Your choice/Hone Claws (or Claw Sharpen in the Japanese's case)
Earth Power (STAB and boost from sheer force), Thunderbolt (boost from sheer force, covers water types), Flamethrower (Boost) and Sludge Wave (STAB+ sheer boost)
I'd say the timid/Modest set is better but it's entirely up to you. :) Go with the adamant/jolly set for higher attack.