A lot of it depends on what you want to do with it. The 50 was the standard for decades but that was on film and full frame cameras. The 35mm is basically the same thing for the DX like your D3100. I have that lens for my D7100 and love it. It is fast and sharp. I think the 50 would not be near wide enough for a basic walk around lens. I would really like something in the 24mm range in a prime. I use zooms most of the time though so not a real problem.
That lens should work great. It is very sharp. Just make sure you shoot in the middle of the range of aperture. At least F8 or F10, That is the sharpest part of the lens and also you will need it there for depth of field