35mm vs 50mm on crop sensor DSLR?

I'm using a Nikon D3300 and looking at the Nikon 35mm 1.8G or the Nikon 50m 1.8G. Not sure what to get?
I currently have a sigma 17-50mm 2.8 lens and a Nikon 70-300mm telephoto lens

Look on youtube. They have several videos on this.
I went for the Nikkor 1.8g. Nice lens!

A very common question. I assume you need something for low-light and/or super great bokeh.
The answer could be one or the other or both depending upon what you're shooting and how you like to shoot it.

For example, a street photographer would go for the 35mm while a portrait photographer would go with the 50mm. My answer is just get both.

You should try this: Take a look at a good sample of the photos that you've taken and see which focal length you've used the most. Then buy the lens with the focal length that you've used most often.

Can you enunciate what you expect the prime lens to do better than the 17-50mm f2.8 HSM OS?

If you have money giving you an itch to spend it, some things that can give good value are:
A good external flash (not cheap junk)
A good tripod (not cheap junk)
A Micro Nikkor 60mm f2.8 AF-S

Note: With a front heavy telephoto, a medium to heavy duty three way pan head may be easier to adjust than a light duty ballhead.

The usefulness of a macro lens is much better when you have the tripod and external flash.

You don't say what you want to use it for.
Do this:
Set your zoom lens at 35mm - take a couple of shots
Set your zoom lens at 50mm - take the same shots.

Which is the focal length that you want?

OR
examine your photos - look at the exif and decide which of 35 or 50mm you use the most.

For what it's worth, I have a 50mm f/1.8 but I find it a little long. I bought a 40mm f/2.8 and that solved my problem. I don't notice the loss of 1+1/3 stops.