On the road, it makes no difference. Bike tyres do not hydroplane, so tread patterns squeezing water out from the center have no effect, unlike car tyres where a v-shaped pattern can have some effect.

Off road, v-shaped patterns will tend to give better grip in one direction than the other. As a general rule, the Vs should point towards the front on the front tyre (to give maximum braking traction) and towards the rear on the rear tyre (to give maximum drive traction) when viewed from above.