Reasons to buy a 50mm lens?

I've had a Nikon D5100 since October now. I'm currently using the kit lens and would like to buy a new lens. What makes a 50mm lens better than a kit lens? Which is better, a 50mm 1.4 or a 50mm 1.8?

The 50mm makes a great portrait lens on a crop sensor.

The f/1.4 costs more, is a little faster, and is more sturdily built. The f/1.8 may be the best bang for the buck in all of photography. Either one will be a step up in performance from the kit lens. You may find the 50mm focal length to be a little constricting unless you enjoy making portraits. On a full frame sensor, 50mm is a "normal" field of view.

Some are looking for spectacular views but 50 mm is a very versatile lens allowing doing from portraits to landscapes; primes of good quality give often better results than zooms. There isn't much difference from 1, 4 to 1, 8 f, just half stop and maybe just a bit of quality finish

The 50mm lens makes a good portrait lens on your D5100.It is also very useful in available light photography due to its fast (f1.8 or f1.4) aperture.

The 50mm f1.4 is 2-2/3 stops faster than f3.5 which translates to a lower ISO to achieve the same shutter speed. If ISO 1600 with f3.5 gives you a 1/125 sec.shutter speed, ISO 250 with f1.4 would give you the same shutter speed.

The 50mm f1.8 is 2 stops faster than f3.5 so using the same situation as in the previous example you could use ISO 400 at f1.8 and get the same shutter speed as ISO 1600 at f3.5.

If your budget allows buy the 50mm f1.4. If not, buy the 50mm f1.8.

It's sharper & faster than the kit lens at 50mm.

Your D5100 does not have a focus motor in the body, so if you want autofocus, you need to buy the AF-S version. If you buy the AF version you will have to manually focus the lens.

f1.4 will give you a little more light & slightly more attractive 'bokeh' but imo it's not worth the extra money.

The 1.4 is better since it is faster. What is the minimum focus distance? The shorter that is the better; you can get up close without having a big price. It is an all-in-one lens: you can shoot pretty good wide angles, and if it has short MFD you can get close-ups too.

Just out of curiosity, why are you thinking about purchasing a lens that is only 5mm less than your kit lens?