Triss and Yeneffer are interesting companions much better than stupid DAI companions like Vivene and Sera....You will also play as Siri in W3 for first time...She is Geralt's daughter..
Some people don't like Witcher games coz it doesn't allow custom character and has too much sex and violence 
I know actually. I started reading the books right after I played the first game when it was released.
I still however stand by my preference of DAI companions because Triss, Yennefer, Dandelion, Zoltan...all these companions have a very fixed and defined back story and there's not much Geralt can do in the games to move them from their own respective POVs. They don't really 'follow' Geralt. Nor does their personality develop over the length of the game.
BW's companions though, despite their back stories develop along with the player character. I find that a lot more engaging. Which is also one of the reasons I prefer Cassandra as a companion compared to Solas.
Edit: Also one of the reasons I preferred DA games was because the overall fantasy setting was more appealing somehow. Thedas felt and still feels better than the 'Witcher' world. The latter is a lot grimmer, grittier and dirtier. I guess and that's not really my cup of tea.