Don't forget to factor in the availability of third party lenses. The best of the new designs are in some cases better than first party offerings from Nikon or Canon -- ie, the new HSM Sigma 35 and 50mm -- though these aren't any cheaper!
Others are regarded as pretty good items at a fraction of the price, like Tamron's 17-50 and 28-75 f/2.8. The Sigma 24-70 f/2.8 HSM seems to test better than the Canon equivalent, but not as well as the latest Nikon standard zoom. In any case considering all these zooms cost from 1/3 to 2/3 what you'll pay for Nicanikon inc's wares, they're pretty good value.
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