This subject is interesting to me because I have loved the 24 1.4G since I bought it five years ago: the color, the sufficient sharpness when needed, the out of focus rendering. It has therefore been with some dismay I have been reading about the Sigma 24 1.4 and how it blows away the Nikon for half the price. I haven't seen any examples from the Sigma but I wonder what I am missing with my beloved Nikon? Since this thread has no examples as yet, for discussion's sake, let me post one of my own. It is cropped for composition purposes so that may defeat my effort to defend the lens I have and give ammunition to the lens I have not.
This photo was shot an hour or so ago of my Crown of Thorns at a window which looks onto my porch and beyond to the yard and woods. It is wide open at 100 iso handheld and while the sharpness does not skirt along the razor's edge it has a pleasing softness (at least to me). No sharpening was done to it. Its inherent characteristics that draw me to the lens are here reflected as best as I can render them. No claims of art are made (unlike the Sigma!), I just think this thread needs a picture or two.
As for the Nikon 24 1.8G, I know nothing about it.