Which lens is better - Nikon 18-55mm DX AF-S, or 50mm f/1.8 D AF?

Right now I own a Tamron 18-270mm f/3.5-6.3
I used to have a Nikon 18-55mm DX AF-S but sold it…

Since you already have the 18-270 the 50mm f1.8 would probably be a better buy. Especially if you do a lot of indoors or low light photography. If you're using a cropped sensor DSLR, you might consider the 35mm f1.8 instead.

If you want a good all-round flexible lens, the 18-55mm is the best since it offers wide angle to telephoto in one and it has decent performance and vibration reduction (most do anyways).

The 50mm is a superb low light lens, but on a DX body it is slightly telephoto due to the cropped image so that is what you have to live with. Also it does not have a focusing motor so does not work on cameras without an in-body focus motor.

If your camera is not a model that has an autofocus motor (e.g. D90, D300, D7000) the 50mm AF-D model won't autofocus. The AF-S model would autofocus, and is reputed to be better. The AF-S 50mm or the AF-S DX 35mm would give sharper images than your 18-270mm lens. What focal length to choose depends on what your use is. You have that 18-270mm, so ask yourself what focal length you like to use and wish you had a sharper version of.

They are 2 different classes of lens, one is zoom lens, one is prime lens… 18-55, you can zoom with it, but 50mm, you get shallow aperture, i don't like prime lenses… I would go get a 18-55 or a 17-55

The 50mm f/1.8 is sharper and faster.

The 18-55mm lens is more versatile.

Which works best for you depends on your wants and desires.

I like the prime lenses. They're usually really sharp and the 1.8 aperture will give you great bokeh and great low-light shots.