I can't comment on the Sigma, but I had and sold the Nikkor 50mm 1.4G after I bought the 1.8G. The latter is better wide open, is more contrasty and has better bokeh. In fact, after having owned or used close to two dozen 50mm lenses of all makes over the years, the only one that beats the 50mm 1.8G is the Leica Summicron-M 50mm, versions 4 and 5.
Kranky, if you love 50's like I do, you really owe it to yourself to try out the Siggy. Can't say that it is better than the 1.8G, but it is really special. I've always got room on my shelf for another 50, and I'm sure I will grab the G at somepoint.
OP and D.Diggler, I am not an expert/photographer so it is hard for me to explain in technical term. Bokeh and background rendering in my opinion is a matter of taste although YMMV. I know there is a technical term to explain good bokeh and bad bokeh. I agree that sigma creates the smoothes bokeh among the 3 lenses but not the one that I like the most. I like the zeiss 50mm 1.4 rendering, not too smooth (busy some people say) but has 3D effect on it. I think the 50mm 1.8G is the closer to the zeiss rendering. That's why I keep it.
I wound up picking the 50mm 1.8G. I looked at a bunch of samples, including those from that Nikon Rumors link that snapsy posted, and it seemed like a great performer. I went to the local camera store and looked at the 3, and it seemed liked the right choice.
Feels odd having a lens sitting in my room and no body to go with it. Monday can't come soon enough.
Monday can't come soon enough. 