i have a tamron 28-200 and the pictures are great much better than what i have seen from the 18-200 ok the tammy isn't a high end either but the price for the money at least is much better than with the nikon. my tammy is a 1:3.8-5.8 macro , a good lens and not so heavy as the 18-200 vr and if you have steady hand you will be surpired the picture quality of it.. and my nikon version works perfect, the only thing you have to lock the aperature ring , but after that it works great and flawless
i also have a sigma 28-200 and whaen i compaired th shots , the tammy was the best and the most fare lens imho . and i use it most on holidays when i think i need the range when not i take the 18-70 dx ed a great lens
2004 DX AF-S DX VR 18-200mm 3,5-5,6 G ED 7,5 11
the last one is the number of people tested it the 7.5 would claim it is good , but if i were you go tammy go .. ( no i don't have tammy shares 
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