Yellow Gold. For me it would be because most of my Cartier pieces are yellow gold and it would match nicely with them. Same with my handbags with tend to mostly have gold hardware. For me the yellow gold is dressy. Good luck with your decision 😀
I prefer the WG because to me, it looks less flamboyant (I can wear it everyday) and more elegant (also great for special occasions), plus most of my pieces are in WG. Choose the one that you'll be able to wear more.
Which looks better on your skin tone? Pull your hair back and put a gold piece of jewelry up to your face. For example, I have an olive skin tone, so I look better in gold. Try them on and step away from the mirror. Turn around quickly to see which one catches your attention!
My vote would be for yellow gold since I prefer it but the white gold looks just as nice! I agree with others that you should select whichever best suits your skin tone. Can't go wrong with either one of these, they are both gorgeous!
I would probably go white gold because I love the contrast that the pop of blue makes. To me the blue stands out less on the YG. I also personally prefer the look of diamonds with a WG setting, but I guess it depends on what you already have in your collection & your skin tone.