I can't decide between the Tamron 17-50mm f/2.8 and the Sigma 17-70mm f/2.8-4.0?

The Sigma is better ergonomically and focuses quieter but doesn't have much reviews and I didn't like the tests so much. Im also not sure if optical stabilization is the same thing as vibration compensation. Everyone loves the Tamron but what do you think? 30mm difference in zoom is something to look at. How are they both optically and for video?