Having a Sting, it will be a little earlier and less angular than the Octane. The Octane in Motiv's medium ball lineup is going to be the true skid/snap motion and it is slightly weaker than the Sting.
The Shock is designed to be smooth throughout and therefore isn't going to be as angular as the other 2 balls. It does have the same hook rating of 50 as the Octane.
If I were building a 3 ball arsenal, I would go:
1) Covert Revolt (a versatile medium-heavy solid, smooth and handles some volume)
2) Sigma Sting (great benchmark ball, versatile on a huge variety of medium patterns)
3) Tribal or Octane (just depends on the motion you're looking for- Octane is slightly stronger than the Tribal)
Those 3 balls will handle probably about 90% of what you'd see on tournament patterns.