[davidmanze]

The Sigma 17-50mm f2.8 OS HSM is better built than your old 17-50mm Tamron. It is a bit more contrasty, it has less problematic CA at 17mm. It focusses more accurately and silently. It offers IS. From what I have seen, bokeh is pretty pleasing too.

 

I wonder which phone offers a standard zoom?

 I've tried both, my copy of the Sigma (S/H) was poor, while trying just about all the F2.8 short zooms (in Pentax inc. the DA* 16-50) I realized just how good the Tamron is, I still think the Tamron nudges it fully open, but it's a close race!

  If I was starting again I'd try a new Sigma knowing I could return it for another if necessary.