I guess instead of linking to another thread, here is my response:
CONS for 18-70/70-300VR
1.) Need to switch lenses
2.) Lack VR for 18-70 (although, one probably don't need VR at this focal length unless at very low light situations)
3.) Slightly more expensive option ($250 (new) + $500 (new) = $750, vs. $700 (MSRP) for 18-200 VR). Although this does not necessarily apply to me, since I already own the 18-70 lens and I don't ever intend on selling this lens.
PROS for 18-70/70-300VR
1.) Better image quality than 18-200 VR (less distortion at wide end from published reports (i.e. photozone.de, 18-200 VR broke the record previously held by Canon 17-85mm IS for being the lens with most barrel distortion!!) and sharper at the tele end (i.e. MTF charts, quite clear difference; 70-300 VR @ 300mm is sharper than 18-200mm @ 200mm)).
2.) Better construction... from the pictures of 70-300 VR, the lens is cammed with much less extension, and I love the big fat zoom ring on the 70-300 VR. Whether the 70-300 VR will suffer the serious zoom creep a la 18-200 VR remains to be seen.
3.) 70-300 VR is a full frame lens (future proof)... see how much the Canon 75-300mm IS lens, introduced back in 1996, is still holding good value in the resale market. This lens was Canon's first IS lens and now after 10 years, the lens is still semi-decent, even after Canon updated this lens with the superb 70-300mm IS late last year. I can probably anticipate using this 70-300 VR lens for 10 years, by which time I fully expect Nikon's FF camera to be released AND affordable.
4.) Lastly, the 18-70/70-300 VR cover more range from 18 to 300mm. The difference between 200mm and 300mm is definitely noticeable. And having two lenses does mean that you don't "put all your eggs" in one basket, i.e. if you accidentally dropped/damaged one lens, you'll still have the other lens (i.e. lower cost of replacement, compared to putting all your eggs in one basket in the case of 18-200 VR).
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Now, in summary... what is my verdict? Well, I am just as confused as most of us are... Some days, I tell myself to go for the 18-70/70-300 VR, other days, I am all for the 18-200 VR and just accept the inherent compromises of the superzoom...
I would definitely appreciate and welcome some rational discussions on this subject... I have preordered both 18-200 VR and 70-300 VR, and I have a feeling that both lenses might be available to me soon (thus, I need to make a decision fast!)
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I shoot with both N i k o n D 5 0 & C a n o n R e b e l X T