Upgrade Help on lens please Nikon?

For portrait pictures? What lens do you guys recommend to get? 17-55mm OR 24-70mm… Please I need help, I use the Nikon D5100.

Neither. Get a 50 1.4 AF-S and maybe an SB-700.

For portrait pictures you do not need, nor want, a zoom lens. You want a prime, or fixed focal length lens such as the excellent Nikkor 50mm f/1.8 lens. Probably the ideal portrait lens will be between 70 and 135mm (in 35mm terms, so your camera needs between 50 and 85mm).In order to find out too much on this subject, read this.
http://www.bjp-online.com/british-journal-of-photography/technical-report/1934957/portrait-lenses