I personally don't use Shao at all but that's mainly because I have AW Minerva, (AW ability improves attack speed) and since both assassinate only during skill and Minerva's skill buffs not only attack but also attack speed, and she has bigger range and higher stats it's just not fair to Shao to even compare lol.

Saki vs Shao
Saki wins: raw stats, attack speed, initial skill timer
Shao wins: cost and range
Melee vs Range slot may be a factor on certain maps

depends on how tight UP is, availability of melee and ranged slots on the field, and the potential need for the "drop and pop skill" ability all blacks, Saki included, have. However, considering most people agree assassinate shouldn't be relied on, for mowing down enemies, unless range and cost are factors and potentially lack of melee slots, Saki wins easily with her vastly superior stats and attack speed



That said, I love my min-cost Spica and if this is your first CR, it's guaranteed and brings her down to -2 (because she comes with a built-in -1) and skill up, so I'd honestly go with that over Saki unless you need/want the black/added deployment flexibility/instant skill/extra scenes she offers.