This varies for every single Pokemon, and EV spreads are absolutely not limited to the two you listed -- in fact, there would be very few Pokemon that use one of the two exact spreads you listed. Competitive play is incredibly broad and varied, so there may not even be an overall "best" EV spread for defensive Pokemon, but most will have something like 252-248 HP, a large amount in either defensive stat and the remainder in the next best spot.