I like them both, but I prefer Triss. Here's why:
She is definitely head over heels in love with Geralt, so much that she is ready to betray everything and even her best friend. Although I haven't read the books, from the sections people posted it is clear that in them her love was one sided, I think Geralt cared about her, just not in a way she wanted. At the end of the books she is left in a pretty miserable state, having betrayed her friends and with the man she loves dead and gone. Enter games, when she found Geralt she must have been ecstatic and with his memory gone and her not knowing what has happened to Yen she saw an opportunity she couldn't miss. I know that for many people this is seen as a shady move, and it is, but I can understand her and it shows me that she is ready to do anything to be with Geralt, even though her love at this point can easily be seen as obsessive.
In TW2 I got a vibe of insecurity from her regarding the relationship with Geralt, knowing his memory is returning and that Yen is alive, she is aware that losing Geralt and even having him resent her for the things she has done is a real possibility, especially after Geralt demanded her to come clean and tell him everything. Despite all that she agrees to help him, but as we latter find out, the Rose of Remembrance also has mind control abilities, I can't help but wonder whether she was honest in her desire to help Geralt regain his memory or is she maybe thinking about doing all she can to keep him beside her under the pretext of helping him. While the game never implies that openly, it is still something I took in consideration. She continues to seem insecure when she asks Geralt whether he wants her to help him find Yen and even if the player continues to reassure her of the love he feels for her she still, at least to me feels insecure about it. What led to their breakup between games can only be speculated but with Geralt memory back I like to imagine they mutually decided to give each other some time and see what will happen with their feelings once Geralt is reunited with Yen.
In TW3 that insecurity is still present and can be seen through the awkwardness that exists among them when they finally meet for the first time after TW2.It seems like Tiss herself doesn't believe Geralt would choose her over Yen. It is clear that her feelings are very strong but she fears Geralt doesn't share them and is reluctant to react. Convincing Triss that you want to be with her, culminating in the moment Geralt declares his love and finally making her believe that he does in fact want to be with her despite Yen's return is very appealing to me. So bottom line, she is ready to do anything for Geralt and while her love is sincere, things she would to for it are not, and for whatever reason my demented brain loves that.
