I've owned both of these for over 2 years each.
1.always takes overexposed shots by 1-2 stops.
2. Great Bokeh
3. 30mm is perfect for just about everything
1. Super sharp and fast focus
2. Bokeh not impressive
3. 35mm is a bit too close-up for everyday shooting (in my personal taste)
I would still get Nikon over Sigma. I rather have faster focus with right exposure.