Nikon d3100 35mm or 50mm lens?

I have a d3100 and only have the kit lens. I'm looking for a good all around lens for trips to the beach, nyc, etc. Should I get a 35mm, 50mm or something else?

Depends on what you need

The D3100 being a crop sensor change the EFFECTIVE focal point.

As in a 35mm will act as an 52mm and a 50mm will act as an 75mm.

This means that the 35mm will be a "normal" lens, aka close to how our eyes see. And the 50mm will be closer to a portrait lens because it is more zoomed in so to say.

So really what do you need, I think on the beach.both lenses have their place but I do suggest to first stick to width. Aka take the 35mm or if you find something wider.something wider.

The 50mm will be a nice portrait lens and that also is useful on a beach.

You do have the 18-55mm lens right? Good! You can actually test it out, put the lens on 35mm and shoot a few pictures with that. Then put it on 50mm and shoot a few pictures with that. Notice how different the images feel, the wider version will look more as we ourself see. The 50mm variant will look more zoomed in!

Again sometimes you want that effect of a bit more zoomed in, pulling it more tight. Other times you want wider!

Self I did buy a Tamron 17-50mm F2.8. Why? It is a zoomlens that replaces the kitlens and has F2.8 over its full range. You'll notice that! It aint a perfect lens, I mean it is cheap think $400 and it performs close to a $1200 lens. Close. It aint a perfect lens. But definitely a good replacement of the standard kit lens.

For your trip to the beach get a Nikon AW110 and avoid risking your D3100. If you do go onto the beach with your D3100, you want to have it in a very good camera case (a good idea anyway) and be VERY careful.

I would buy the 50mm even on a cropped camera.