In Guardians of the Galaxy, Thanos calls Gamora "his favorite daughter" in his meeting with Ronan. He even says this in front of his other adopted daughter, Nebula.
This doesn't make any sense for a couple of reasons. For one, Gamora eventually betrays Ronan and Thanos, while Nebula faithfully serves them throughout. Obviously at this point, he doesn't know that yet, but Gamora clearly has a lot of deep seated resentment of Thanos. Another reason this seems weird is that he says this in front of Nebula. He still needs her help, and surely insulting your family like this can't be good for morale.
Is there any reason that Thanos would call Gamora his favorite? Or is it possible he's just saying this just to offend or motivate Nebula?
If there's an MCU-level Canon answer, that would be awesome. But since I don't think it exists, an answer from the original comics or the expanded universe would suffice also.