What is the sharpest normal zoom nikkor lens?

When i say normal zoom i mean 16mm-200mm sort of range. I have a d5200 and i want to get a lens that takes really sharp photos, specially portraits. I have a couple in mind, like the 18-105, 16-85, 24-85, 18-200,… Etc. But like i said sharp images is all i care about, NOT THE ZOOM. And i want a NORMAL lens, not a wide or single-focal length lens. By the way, is it a good idea to get an fx format lens (like the 24-85) for a dx camera? If so, what are the benefits?

It keep eye well

The old 24-85 mm f/2.8~4 is a very sharp lens as is the 24-70 mm f/2.8

The 18-200 mm is sharp, but more of an editorial lens and while not unsharp, it is good enough for creating images for publications

If you buy FX lenses, you will have what you need when you eventually buy a camera like the D600.

Of course DX lenses can be used on Nikon full frame cameras, so you do not have to worry about that aspect.

I have used the 24-85 mm, 24-70 mm and even the 18-200 mm lens when shooting portraits. All three work fine, however the 24-70 mm f/2.8 ranks as the highest performing of the three, followed by the 24-85 mm when tested in a lab

This is a very complicated question to answer.

It depends on the aperture you would be using the lens at most of the time also.
Sharpness in the center or sharpness from edge to edge?
Sharpness at a specific focal length or sharpness throughout the entire focal length range?

What is your budget?

I recommend the 24-85 or the 70-200.

Its fine to get an FX lens because you can always use it on a FX body, so room to upgrade. On a DX body more of the lens center is used and therefore it is more sharp corner to corner and there's less vignetting in the corners as well. Obviously since you are using it on a DX body it will have a different field of view than on an FX body. ( Multiply lens focal length by 1.5 for Nikon.)

Keep in mind you can sharpen your images in post and in many cases you can't see slightly soft corners on an 8x10 print viewed from 18 inches away nor can you see it on a 1000 pixel jpeg posted on Facebook. There's a difference between scientific data and realistic application.

In the range you have used as examples, I think the 24-70 f/2.8 is the class leader in sharpness. I want one. But… I decided to hold off and see if they bring out the lens with VR. I guarantee that they will do that 3 days after I buy one without VR. If VR comes out on the 24-70, two things will happen. The non-VR price will drop and there will be an influx of nice used 24-70s on eBay and at dealers.

For now, I have diced to stick with the new 24-85 f/3.5-4.5 VR that came virtually for free with the D600. There's more distortion with this lens than others, but the camera fixes that nicely for jpgs and CS6 fixes it nicely for RAW images. The distortion is not even a problem for most subjects.

You can't judge a lot from this size images, but I have a few samples from the 24-85 VR lens on Flickr.

Don't confuse this with the older non-VR 24-85. VR will go a long way towards giving you sharper images when you are hand-holding your shots.