You need to look at tests for those lenses.
Here is a European site that does extensive testing on lenses:
http://photozone.de/reviews
..
which lens is best
Nikon Nikkor AF-S 55-300mm f/4.5-5.6G ED VR
or Nikon Nikkor AF-S VR 70-300mm f/4.5-5.6G IF-ED
?

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