15 attack and defence in my opinion. In majority of cases they'll perform the exact same, the difference of 2 stamina IV at level 40 is only a 1 HP difference, but if the extra defence could mean the difference between reaching a defensive quick move breakpoint, reducing 1 damage on every quick move would result in higher survivability.
You can't go wrong with either, there'd be next to no difference compared to a perfect one, plus you could just power both of them, give one Solar Beam and one Earthquake.