The sigma 30 f1.4 is a DX lens and was designed for usage on a crop sensor... The nikon 35 is a FX lens and will work on full frame. of course this is moot if you are in Dx land and have no desire to upgrade to FF.
I owned the 35mm Nikon f2 and it was a fantastic lens. I would not hesitate to recommend it.
I hear rumors on the forums that the sigma has problems from one copy to the next...
how often do you need f1.4? my copy was a good one but the bodies i had it on were not fast enough in AF for what i needed to shoot so i switched to the D3 and the 50/1.4 instead. on DX, the 35/2 is decent enough but not fast focusing. the Sigma is a bit faster. the Sigma is sharper in the center until stopped down a fair bit. at f11, there isn't a lot to choose between the two for image quality on DX. on FX, i quickly sold the 35.
