Riven is best if you can pull your Fast Q combo in all scenarios. Given that, I have adapted my runes towards the Chinese/Korean Meta for Riven. Attack Speed Quints are much better for scaling against many things that may be present due to the meta changes, and 6.8 AD in the early game doesnt make a drastic difference. Frozen heart, Malphite E, or even CC that forced you into a situation of winning an all in or dying. Best example is against a Maokai who is going in for the kill. All in all its mechanics and how comfortable you are.

Thanks.
P.S. (Im new to guide making, working on it)