You'll need to specify which version of the 28-200mm Nikkor you mean - is it the older "D" model, or the more recent "G" model (both are now discontinued)? The two are pretty different in design and image quality.
I haven't used the 18-200, but I used the 28-200G quite a bit on my D50. It has a short close-focusing distance and can almost be used as a macro on a DX body. Obviously the 18-200 has the advantage of VR for tele shots and those extra 10mm on the wide side, but not everyone needs those - in good light and especially on the telephoto end, the 28-200G performed surprisingly well for what it cost.
Compared to the 28-200G, the 18-200VR is a bit of a "horses for courses" comparison. There's no doubt that the 28-200G is sharper at 200mm than the 18-200VR. The newer lens is also better at the short end, although not by as large a margin. On the other hand, the DX has VR, which for many more than makes up for the optical difference at 200mm. A blurry, shaky image sharply rendered is not better than a not-as-sharp but in-focus and non-shaky rendition!
The 28-200G is also an FX lens, in the event that FX becomes an important consideration.
_____ Brian... a bicoastal Nikonian and Team Member
My gallery is online. Comments and critique welcomed any time!
I haven't used the 18-200 DX VR lens. I do have the 28-200 G lens (which is an full frame lens - FX format). I use it on my D700 (12MP) and find it a great travel lens, small, light weight, great range, excellent performance (for me). Best of all, its inexpensive.
No, it doesn't have VR, no it doesn't have the latest lens coatings and on a DX body, its not very wide.
I've owned and used both versions of the DX 18-200. I did like them better than the 28-200 that I previously owned. However, after getting a 28-300, I would never consider another 18-200. Not that either were "bad", the 28-300 is just "better".
Of course you "must have" a 10-24, 12-24 or 14-24 to cover the wide end. NAS says you must have/deserve them.