Tareq wrote in post #18113945
So Tamron and Sigma are trying to match most of Canon/Nikon long zooms, good news, i have Canon 100-400 mk1, if i will sell this then i am not sure which lens i should get for Wildlife Safari and birds as zoom lens.
I have had the Tamron (do we call it G1 now?) for a couple of years, and I have no complaints at all. I had the 100-400 mk1, and the Tamron gives me as good results as I ever got with the Canon, with an additional 200mm on the long end. I know that some people (who will certainly chime in here) have had problems with the AF on the Tamron, and to avoid that possibility I sent mine to Tamron for the firmware upgrade addressing these issues. The fix was free, I was without my lens for about a week, and I have had no AF problems. I have a friend with the Sigma C, and he is very happy with it. I don't think that there is much of a difference in IQ between these lenses.
The Sigma S is a different beast, and some may say that it is not really in competition with the other two. However, the head-to-head comparisons of these three lenses have found little to no differences in IQ. And the S costs much more (although you get more weight for your money).
The new Tamron lens has the appearance of being a meaningful improvement. The optical formula is updated, so it is not the same glass in a new tube. The changes appear to emphasize performance at the long end. BTW, that tube is metal, not plastic. VC performance, and both AF speed and AF performance were targeted for improvement. Weather sealing throughout the lens has been added. And then there are many features that will simply make the lens easier to use. I expect that a year from now, many buyers who would have selected the Sigma S over the existing competition will be buying the G2 instead, assuming that its performance matches the specs.