The-Digital-Picture has completed their exhaustive review of the brand new Tamron 24-70mm f/2.8 VC G2 lens. A direct competitor to the Sigma 24-70mm f/2.8 DG OS Art lens.
From TDP:
Putting the Tamron 24-70mm f/2.8 VC G2 Lens to the test … the wide-open aperture center-of-the-frame results at f/2.8 are very sharp at 24mm and 35mm. By 50mm, a slight degradation is seen and at 70mm, center-of-the-frame results are somewhat soft at f/2.8. In the wider half of the range, stopping down to f/4 makes little difference in center-of-the-frame sharpness and really, none is needed. In the longer half of the range, especially at 70mm, stopping down to f/4 brings a very significant improvement in image sharpness. This lens is very sharp in the center and mid-portions of the image circle at f/4 with little improvement seen at f/5.6 aside from the mid-frame areas showing slight further improvement at 70mm. Read the full review
We have lots of options at this focal range from Canon, Sigma and Tamron and it may be hard to choose which way to go. One thing is for sure, Sigma and Tamron have proven that the market wants a stabilized 24-70 f/2.8 lens and it might be time Canon answered the call as well.