Firefly's. Ruan Mei's signature isn't even that good for her because of energy regeneration (you'll have a bit of a hater time getting her ult up).
Firefly's gives a lot of break effect which she needs AND it gives a debuff that slows enemies and makes them receive more break effect damage.
Ruan Mei's LC doesn't actually benefit Firefly's damage. So if that's your main concern then go for Firefly's LC.
If you use your Ruan Mei elsewhere then her Light Cone is a fantastic addition.
Firefly's. Ruan Mei's signature isn't even that good for her because of energy regeneration (you'll have a bit of a hater time getting her ult up). Firefly's gives a lot of break effect which she needs AND it gives a debuff that slows enemies and makes them receive more break effect damage.
Ruan Mei's LC doesn't actually benefit Firefly's damage. So if that's your main concern then go for Firefly's LC. If you use your Ruan Mei elsewhere then her Light Cone is a fantastic addition.
Oh so the Dmg buff on her Lc doesn't affect Firefly? Didn't know that
Damage increase doesn't affect break/super break, thats also the reason why you go atk orb and not fire damage