What Nikon lens should I upgrade to?

What Nikon lens should I upgrade to?
I'm starting to full body shoot basically photoshoots. I've had my kit lens for about year and i need to upgrade I've learned a lot from my kit lens. What lens should i get I've been doing many photoshoots! I have a Nikon D5100… Anything helps I was planning to get a d700 for my primary camera then my D5100 for back up? I had bought the camera separately then got my kit lens. So this camera is about 2 years old. I'm planning on getting a 50mm 1.4 or a 24-70mm AF-S, to get some money then get the D700. Will the 24-70mm af focus?

Any Nikon AF-S lens will auto focus on your D5100. The 50mm f1.4 makes a good portrait lens on your camera. Its also great in low-light situations.

You don't really "upgrade" lenses per se. You either replace them, or add to your collection

that being said, the 24-70mm f/2.8 is a beast. Definitely one of Nikon's best lenses for portraits. It will autofocus on both the D700 and D5100