What would be the best hair to use for victoria 4,2 in Daz Studio 4.2 Pro if I was trying to create a photo realistic render?
ANY, it will all depend on how much about DS and 3D rendering you know as to how close to Real you will get. Way to many subjects to cover in one post but it will involve Lighting, Texture settings in Surfaces, Uber this that or the other thing depending on what you use and many many more things. Learn to walk before you try to run. IE learn as much as you can and then use what you learn often. In four years I've only done TWO renders that came CLOSE to Photo real.
Somewhat difficult to give a definitive answer to that question, considering that in the DAZ 3D store alone there are over 900 items in the hair category, and that is without looking in other stores.
You make no mention of style etc, those details could help.
That's a very good question. I haven't rendered anybody with hair in a long time, because it's just too slow. Essentially look at the promos and exclude those with baked on highlights, unrealistic textures, or insufficiently defined transmaps (look for lose strands and see if the hair fades realistically or not). If you are in the Platinum Club take a look at the hair in the Plat Club (e.g. Jade Hair, Classic Rolled Hair, Trixy Hair all look good to me). I also like a lot Neftis models but the texture, although very good, is of too small a size usually. Reby Sky Elite Hair is also probably a good choice.