There is no way to completely resolve the books and games at this point, because in some instances it's best to let the books dictate design, and in others the game lore. So it has to be a fluid process for the devs and for the player. In this instance, I think being an RPG first and foremost trumps the books, so for me Triss is the right choice because Yen is late to the party and is a volatile partner. Indeed I can surmise from both the books and the game Geralt's relationship with her is essentially a curse and that anyone is better than Yen. Is Yen a fascinating character? Yes. Will Geralt always be a sad beta male with her? Absolutely.