35mm nikkor prime or 55mm nikkor prime, which is better?

Looking for a prime for low light and portrait, same price, which do you recommend ( both g series)

Low light performance depends on maximum aperture. The lower that f/number, the better for low light. I assume they're both f/1.8.

On a crop sensor dSLR, if you want a normal or standard lens (one that approximates the angle of view of human eyes) which you can use for almost anything, get the 35mm. The 55mm would be good for portraits and closeups as it would act as a short telephoto in this case.

On a full-frame dSLR, the 55mm would be a normal or standard lens and the 35mm would be a wide angle lens. Choose which you think would be more useful to you.

I would suggest you to go for the 55mm one. That is better suited for portraits. Primes are always more or less good for low light because they are at least f/1.8 if not 1.4 which is quite fast even in dim conditions.

Depends on what you want it for.

The 35mm lens is a DX format, while the 50mm lens is FX or DX. This would be important only if you have a FX format camera such as a D3 or D700, or plan on upgrading one day (but you would probably want a 50mm f/1.4 if you did that).

The 35mm lens on a DX camera wile it will result in an effective focal length of 52mm, it will retain the perspective distortion characteristics of the 35mm focal length. For this reason, it is not really suited for portraiture.

If you have a D90 or above, also consider the AF 50mm lens, which is every bit as good, and is less expensive (not that the other two are that expensive). But as the AF 50mm lens requires a focus motor built-in to the camera, which means it is most suitable for a D90 or above.

Here is a comparison of the perspective distortion of the 35mm vs. 50mm lenses:

http://www.althephoto.com/lenses/35mmprime.php

Notwithstanding the perspective distortion, the 35mm will give you a bit of wider angle. Otherwise, both lenses are good.