Sigma 17-50 or Tokina 16-50 which one ?

I've just seen the new sigma 17-50 and so far I read lots of great comments on it.
Now as tokina cheaper than sigma, is there any reasonable factor to choose sigma over tokina and pay more 200 bucks ?
I know sigma has HSM and OS. However tokina's AF system is silent and fast adequately, at least as far as I've read. Moreover OS system is not really necessary for a lens with constant f2.8 aperture value. Okay it maybe useful but not a must.

While the case like that what would your choice be.
Really need some logical and convincing reasons to make my final decision.

By the way, I was considering the canon 15-85. Whereas it's a little out of the comparison due to its aperture value and range. However if you have experience with this lens please feel free to write your opinions as it's in the comparison as a part.

Thanks in advance

The Tokina is quiet but it isn't HSM, Its the screw drive system. The Sigma is a new design. I would go with the Sigma. The only silent Tokina is the new 16-28 2.8 full frame lens.

lzooml wrote in post #11274260
Moreover OS system is not really necessary for a lens with constant f2.8 aperture value.

This isn't necessarily true. If the shutter speed is low enough, then OS becomes essential.

I'd get Tokina 16-50. The price is 200 lower, yet the quality is superior, not typical plastic feel like Sigma and Tamron. At this focal range, OS is not that useful, and it will drain your battery quicker.

While the Tokina is built like a tank, the Sigma is an EX lens - all metal barrels. OS can be handy on any lens if the shutter speed is slow enough. One has to weigh the differences to determine which suits one's shooting styles:

Tokina: exceptional build, 1mm wider

Sigma: HSM focusing motor, OS

Optically, the lenses are a wash.

Also, where are you seeing the $200 difference? At B&H, the lenses are $120 apart.

Tokina all the way. the best all-walk-around lens i have ever tried. compared to 24-70L, 24-105L, 17-55IS, and any of the other third party lenses...

only thing is hard to find one. i might sell mine though as i have decided to abandon DSLR for awhile...and might come back to it with FF body instead.

Thanks for opinions, any other ones are welcome.