Shivv or PD on vayne?

Logically thinking, it really depends on your current/target AD and ASpd.

• If your Vayne is inclined to hitting harder(Having a higher AD or planning to use Infinity Edge after) then you should take Phantom Dancer since the crit chance is much higher, and it gives you faster mobility and attack speed. This maximizes the Damage output.

• If your Vayne is more of an ASpd build(maximizing the Silver Bolts), then you should take the Statikk Shiv since it will proc the passive more.

They're similar enough in power that choosing one over the other probably won't affect your damage too much. However, depending on what your goals are in game, you might prefer Stativ Shiv or Phantom Dancer. For example, Statik Shiv would probably be an excellent choice for split pushing whereas Phantom Dancer would be a bit stronger for dueling 1v1.

With Vayne, PD is my 100% buy every single time. As her early game is worse than an underfed Kha'Zix, buying SS is a very quirky way to build Vayne. Sure, you get more burst, but you need the AS to pop 3 stacks quicker. Especially when your W is maxed, your true damage of 8 PERCENT OF THE TARGET'S MAX HEALTH will bowl heads compared to the maximum of 250 it can do on a target before having to AA around 9 times to get that 100~250 damage.