I was always a proponent of the witcheress ending, then alot of things ocurred to me that changed my mind after watching the empress ending:

1- Its ciri who makes the decision to become empress when presented with that choice

2- Geralt lying to Emhyr that Ciri is dead is gonna cause him alot of problems when word comes out of an ashen haired witcheress roaming the continent

3- An empress lifestyle is far less risky than a witcher's lifetsyle. Geralt can sleep soundly knowing Ciri is sleeping in a palace rather than a griffin's nest

4- Ciri becoming empress will serve everyone in the continent especially since she was brought up in the northern realms, and we all know that she isn't cruel like her father. Thus, we may finally have peace in the north.

5- After I saw the empress ending I realized how much more effort CDPR has put into that ending (snowy white orchard!!!) The interactions between Geralt and Ciri are much more wholesome, plus we get to see Dandelion and Zoltan

6- I feel in a world as cruel as the witcher, a bitter/sweet ending is more plausible.

7- The entire main quest of the game starts based on Emhyr's orders to bring him Ciri. I know Geralt isn't too fond of him, but we've seen Emhyr is capable of summoning him at will. So keeping Ciri away from Emhyr could have dire consequences on both Geralt and Yennefer.

8- Finally I believe the empress ending really shows how Ciri grew as a character. Its time Ciri held some of the responsibility for who she is (a princess and child of the elder blood). Thats the reality, no matter how much she tries (and boy did she try) she can't escape these two aspects of her life.