All 3 games have their own set of flaws and highlights, some doing particular things better/worse than the others. But it would say they are all overall really good.
When it comes down to a favorite i dont really have one, but i can easely say that the first two games are supperior in most aspects to The Witcher 3.
While overall i think TW3 is still a good game and i did enjoyed my first(and only) playtrough of it, there was much left to be desired. It felt more like a stand-alone tittle rather than a sequel to the two previous games. It was also filled with unnesesary fan-service to the books that felt out of place and did not developed the story in any postive way.
The gameplay in TW3 has a better flow than previous two tittles, specially with features like jumping, horse riding and swiming. And the animations(specially facial) are top notch in comparison to anything else out there.
However, the story was overall a big letdown full of cliches and black and white choises, and the oversimplifications of things like alchemy was very dissapointing, so was the inclusiong of the MMO style leveling and itemization. I also miss many immesion and QoL details like animations for eating, drinking, etc, something that the previous two Witcher games, or the newer RDR2 and Kingdom Come Deliverance do way better.
So all in all TW3 being the biggest and most expensive in terms of development of the 3 does not really equals to it being the better product, if anything i feel it is the oposite. The previous two tittles are better becouse they were more focused and did not try to do everything at once like TW3 does.