You asked
Nikon 18 200mm f 3 5 5 6 vs tamron 18 200mm f 3 5 6 3 di ii vc?
I don't have a page for the Nikon 18-200mm f/3.5-5.6, so I can't give you a fair side-by-side. I'd rather not guess at its specs. Check the gear catalogue for its page before you decide.
The Tamron is covered: Tamron 18-200mm f/3.5-6.3 Di II VC. It's a stabilised, autofocus APS-C zoom for Nikon F and Canon EF. On a Nikon APS-C body it frames roughly like 27-300mm on full frame, which is a lot of reach for a travel lens. It only works on APS-C bodies, or on full-frame Nikons in crop mode.
If you tell me which Nikon body you own, I can help you judge whether the Tamron's reach is worth its slower aperture at the long end.
Written by Claude from this site's pages.