I like the 70-200 f/2.8 L-IS USM. Here's an unretouched shot (no skin softening,etc) made on the 12.8 MP Canon 5D "Classic", done at f/7.1 at ISO 400, lighted using one 40 inch Lastoline umbrella, one door-sized white reflector, and a gelled background light.
What I like about the 70-200 zoom lens on a full-frame camera is that it allows me a wide range of ANGLES OF VIEW BEHIND the subject...at longer focal lengths, the angle of view BEHIND the subject grows much,much more-narrow than the angle of view is when using a shorter focal length from a closer camera-to-subject distance. This is one of the MAIN reasons a 50mm lens is not nearly so handy in-studio as it is outdoors; it does two things I dislike: 1-A 50mm on FF forces me to be far too close to the subject, thus exaggerating the SIZE of arms or hands extended toward the camera in a major way, as well as
slightly exaggerating nose size and 2) It shows so much angle of view BEHIND the subject that the edges of a nine foot-wide seamless paper or a muslin are often in the picture area. However mjuch I dislike the 50mm indoors for studio-type shots, for "environmental" portraiture, a 50mm or other shot lens on FF is a different animal
,entirely...it SHOWS
the environment to a much greater degree than a longer lens, shot from farther back. So, like so many things, the 50mm is a double-edged sword. I LIKE Canon's 85mm f/1.8 EF for its small size, and its sheer EASE of use....it's lightweight and easy to hand-hold, and people are not intimidated by it, so those factors alone make their 85/1.8 a nice studio portrait lens. But the
focal length flexibility of the 70-200/2.8 makes it what I consider to be "the best" portrait lens. For outdoor work, it's even better!!! MUCH more reach and much,much more "Control" over angle of view, image size, and depth of field than with ANY prime. And adequately sharp, focuses fast, and has nice bokeh also.