So admittedly, I’m not far into the game and only played a single Ciri segment thus far as well as read a few in-game books. (Please don’t spoil me.)

My main point is that she’s more talkative with more personality shining through. Geralt usually answers in a short straight forward fashion and does not seem to care either way what happens to most things. Ciri on the other hand showed a clear alignment.

There’s also more innate conflict about her character with her being the daughter of the Nilfguardian king as well as the Elder Blood thing (I’ve only read the book of the same title). While someone already spoiled me that she gets kinda OP because of the later, I think there are more options for interesting power progression with her. I’ve read all skills Geralt can learn and I’m quite sure I’ll be playing in a similar way towards the end of the game as I do now, just popping more potions. In addition, the only innate conflict with Geralt so far (and from what I remember playing WItcher 2) is whether to romance Triss or Yennefer (and I’ve got no horse in that race, neither of them is my type).

Lastly, while it wasn’t a plot point in Witcher 3 yet, Geralt does lose a lot of points for being a (former?) amnesiac.

My stance could change, but that’s my current view about 15h in. Currently doing the Keira questline with the ghost lamp.