Hi A100, and welcome to the Camera Labs forum!
You've certainly read the review here: http://www.cameralabs.com/reviews/Tamron18200mm/
or have a look there
. The 70-300mm is reviewed over here
The 70-300mm is a tad soft at the long end. The best option seems to be the new 18-250mm (tested there
) as it has the better IQ than the 18-200mm.
The benefit of the super-zoom is that you don't have to carry (and switch between) two lenses, so you don't miss a shot and don't get dust into your camera.
Thomas (beware: Nikon-fanboy and moderator!) My Lens Reviews
, My Pictures
, My Photography Blog