Traditional advice says that prime lenses are best for portraiture for many reasons, particularly a wider aperture and better sharpness. Nonetheless, modern zoom lenses can offer very high image quality coupled with increased flexibility, and that can cause some photographers to reach for them before a prime lens when doing portrait work. This video explores one photographer's experience with both.
Coming to you from Manny Ortiz, this video explores the benefits and drawbacks of using prime and zoom lenses for portrait work, specifically an 85mm prime and a 70-200mm zoom. Primes are lauded for their sharpness and wider apertures, which provide the ability to isolate the subject with a narrow depth of field and work in lower light conditions, but the tradeoff is the inability to change your framing without physically moving (or changing lenses). For example, notice in the boardwalk photo how Ortiz is physically unable to get closer (lest he learns how to walk on water), and the 85mm leaves him having to crop in quite a bit. It's very much a matter of personal preference, and depending on your style of work and needs, you might require one over the other. Which do you prefer?