This is a question often asked by many but the answer isn’t a simple one. It depends on many factors such as budget, personal style and make of the camera. There is also the focal length and sensor size to take care of.

There are plenty of lenses in the market but which one is best suited for the type of portraits you click?
With all the money to buy a lens, professional portrait photographers can buy Canon EF 85mm f/1.2 or

Nikon 85mm f/1.4G but it may not fit everyone’s budget.

There are still many options for others to pursue.

Fixed length lenses are affordable and are capable.

What is the feature of a good portrait lens?

Focal length is one thing to consider. Go for an 85mm if you have a DSLR like Canon EOS 6D or Nikon D750. With this you can capture half length portraits from a distance of around 3m. For an APS-C camera like Canon EOS 750D or Nikon D3300 an 85mm should be able to help capture head and shoulder photos from the same distance. It also allows you to slightly compress any prominent facial feature.

Prime lenses offer superior image quality than zoom lens and this is due to their wide aperture which varies from f/1.4 to f/1.8. With this range you can blur out images in the background to highlight the person in the front.

Some of us may have a kit lens. That too is good enough to click portraits.

One has to remember that prime lens is good for portraiture. It has a maximum wider aperture than a zoom lens covering the same focal length. If capturing someone in low light this is useful.
They also produce better quality images.

If shopping for lens on a budget, go for a prime lens.
But usually a good lens will cost you some money. So, decide your budget and shop accordingly.

Definitely the more costly ones have added features which are missing in the ones that are lower priced. That’s a call you have to take since the image quality will differ too.

But the camera lens will last you for many years, about a decade unless there is some accidental damage.
When choosing lens, it is also important to think of the sensor. Instead of going by focal lengths, it is best to categorize lenses and then decide which model is suitable.

A wide angle lens will distort your picture if you try to click a close up portrait. They are good when you also want to include a bit of the surrounding.

Normal lens is fit for a full-frame camera and they are about the same as the human eye but not exactly.

They can also be used for portraits and are mid-way between wide-angle and short telephoto lenses. Use them for close-up portraits.

There are also short telephoto lenses and telephoto lenses.