Test reports are a good guide - but will probably confuse also. It will depend on the lens rather than manufacturer. I notice on the 70 ~ 200mm lens tested the Tamron clearly beat the Sigma and Nikon. On the 18 ~ 200mm the Nikon was marginally better - but at nearly double the price. The Sigma and Tamron were equal with one slightly better in one area and the other better in another area. I suspect the variations will continue for different lens.
I use the Tamron 18 ~ 200mm as a walkabout lens and a neighbour - a member of the RPS and judge - uses the 18 ~ 270mm Tamron.
I have the Tamron 70 to 200 and am very pleased with it.I went with that lense because of reviews,price and warranty.Six years better than any other lense out there.Image qulity is pretty good you should be very pleased with this lense.
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