Which lense is better, the 50mm or 35mm?

I've got a Nikon D3100 and looking to do portraits, so i've been looking at some lenses that are said to be good portrait lenses. I'm stuck between the Nikon 50mm f1.8G or the Nikon 35mm f1.8G and wondering which one is best.

Your camera has a cropped sensor. For the D3100, for PORTRAITS, the ideal lens would be the 50mm. This will give an effective mid telephoto focal length of 75mm, which is a decent length for portraiture.

First - the word is spelled "lens". Lose the 'e'.

Second, the 'best' lens is the lens that allows you to produce the work that you want to produce. That means that you have to decide which is 'best' for you - there's no objective best.

That said, conventional wisdom in photography is that portraiture should be done with a lens that has a focal length that is slightly longer than 'normal'.In 35mm, for example, the 'ideal' focal length for portraiture is in the 80-100mm range. The reason for this is that the longer focal length allows a head-and-shoulders portrait to be done from a slightly greater distance, which means that there's less risk of facial distortion. If the focal length is shorter than normal, portions of the face that are closer to the camera will appear larger relative to portions that are further away from the camera, and this can be rather unpleasant. Think exaggerated noses.

The D3100 has a 2/3 scale sensor - that is, the sensor is 2/3 the size of a conventional 35mm film frame, and means that the effective focal length of lenses used with that sensor is 1.5 times the physical focal length. A 35mm lens therefore appears to be about 52.5mm, while a 50mm lens performs like a 75mm lens. On that basis, the conventional choice would be for the 50mm lens with its apparent 75mm effect.

Have to agree with Steve, for portraits, but not much else, the 50mm f1.8 on the cropped sensor is king, but the 35mm f1.8 will be a more useful general purpose lens. Basically for most things EXCEPT portraits (the 35mm will distort features especially when used close to the subject).

Because the D3100 has an APS-C Sensor, it will give a 1.6x crop. This means a 50mm lens will turn into somewhere around an 80mm lens. A 35mm lens would be more like a 56mm lens. I would go for the 35mm lens. You would need to stand quite a bit back with a 50mm lens, but 50mm's give outstanding bokeh. Also, your budget matters. A good 35mm f/1.4 is £900+ pound, such as the Canon 35mm f/1.4L lens. A 50mm, like the Canon f/1.4 USM is £325.So, I would go for the latter lens, it is pretty brilliant.
Also, those criticising the asker's spelling of "lens", don't. "Lense" is an alternative spelling of "lens". I have seen "Lense" spelt like that in shops.
Hope I could be some help, anyway.