Hi,
I can't make up my mind on what to buy.
Nikon 50mm G 1.8 @$299
Nikon 35mm G 1.8 @ $ 650 ( used )
Nikkor 23mm AF 2.8 @ $295 (Used)
All in Australian dollars.
I am looking for a light weight lens to carry around all day on my 610, for street & landscape photography, occasionally with people included.
I need it to be fast also as I like shooting the above in low light & at night, both indoors & out.
I also have a limited budget of under $1000.
Any advice would be much appreciated.

I work alongside them at major press events and news events across Asia. They don't have "proof sheets". They shoot everything they think might be of interest to their editors, and why not? In fast moving events one never knows what will prove to be valuable. Have a look at my raw footage as a news video shooter sometime. I roll on EVERYTHING. What is not used can easily be discarded. It costs only the electricity to charge the battery and format the card. What is important is to have the shot that is needed. Tidy proof sheets are useless if they don't contain the right image, and news photogs do not have the luxury of setting up their shots.

In that case you might be missing out on one heck of a gift. Sigma's "Art" series lenses are not your grandfather's Sigmas, they are whole other kettle of carp. Every Art series lens I've handled is better made than the Nikon equivalent. I traded a Nikon 17-55/2.8 DX for my 18-35/1.8 Sigma, and it makes the Nikkor feel seriously underbuilt as well as putting it in the shade optically. I was staying away from third-party lenses just like you - Nikkors only, please - until I started doing some reading. I discovered that time has marched on, and so has Sigma.

To word this correctly, any lens on a DX camera will give you the magnification of 1.5X, but a 50mmm lens will not act like a 75mm, because, yes, you get the magnification, but the perspective is still that of a 50mm lens. Think of it this way and the proportions are not accurate but for understanding. Putting a 50mm lens on a DX camera is like putting the 50mm on an FX lens and blowing the photo up to an 8 X 10 photo. Now take that 8 X 10 and cut it down to say a 5 X 7 photo. It has a smaller angle of view and appears to have the telephoto effect, but the perspective is still that of a 50mm lens.