Well i went for Triss the first playthrough but it was kind of a close call, however after doing some digging in the novels, i can say that a lot of people would've gone for Yen instead, myself included. Like the game's canonical relationship is presented as Yen and Geralt, since they are actually the main characters in the novels, where they had like years of relationship with eachother, filled with all the hard things in it. Triss in the novel was more like a side character besides a short part where she had a big role.
Like the novels really gives her the proper complexity of the mother figure she is in the game. Whereas the game she is shown to care about Ciri to the point where she doesn't let literally anything get in her way, even Geralt at times. And i feel they made her way more of a bitch in the game than she really is, so it was the pretty obvious choice why me and many others chose Triss over her, even though i knew Triss kinda took advantage of Geralt's amnesia fully knowing he was together with Yen. Besides, Triss seems to be more like a sister figure to Ciri than anything else.
Trust me, read the books because the game does not do her any service compared to her portrayal in the novels.
Oh and yeah, don't romance both of them in the game because... let's say Geralt would be a really good Jerry Springer guest lmao.