Anyone got experience using both of them?

Which one should I get to upgrade my kit lens of canon 18 55?

Tempted to get prime lens as well. Primarily Gonna use it for travel and street photography (walk around). Portrait gonna be secondary.

Tamron 17-50 VC I had own it before.

The lens was great on sharpness but slower autofocus speed.

Sigma 18-70 OS maybe good but in term of sharpness and aperture still weakness than Tamron 17-50VC.

You can find out more here for my own info.
http://vintagephotograph.weebly.com

im using the Sigma 17-70mm F2.8-4 DC Macro OS HSM on Nikon. Apparently this is the never version with Contemporary class. I'm not so sure about the Canon edition but I could say this is a great lens for general use.

On the net, I see that many say sigma better but when I go shops, most of them say tamron better

Walk in shop and test accurate autofocusing for sigma before pay money.

from what i read and surveyed from websites and shops is that previously there is a period where sigma did poorly on their lens especially the QC part. But after that, it seems that they improved the build quality and QC on the new line/range of lens (contemporary, arts,sports).
but all and all you need to read enough reviews (read few to prevent some bias reviews) and test it enough at the shop before buying.

There is no clear better between those two.

IQ, sharpness, colour/contrast: Seems like reviews say Sigma is slightly better. But they are still very close in this section. Too close you'll be wasting your time pixel peeping. But if you really care about IQ that much you might as well get the Tamron 17-50 F2.8 non-VC.

Autofocus: Sigma clearly wins. The HSM is quieter, faster and hunts less in the low light. Tamron's AF is louder and slower.

Image stabilization: Tamron's VC is just the best image stabilization for DSLR. Although its loud and have to wait for it to settle. It freezes the image nicely. VC tech is also high praised for video. VC has a lot of praises even from the nikonguy Matt Granger in youtube, who got very impressed by it.

I got the Tamron 17-50 VC and quite pleased with it. And for low light AF I use a flash with AF beam so no focus hunting problems there. And that VC does help a lot in hand held video.

thanks for the in depth review. some say the sigma one is almost as good as the canon 17 - 55 which make me attracted to it previously but tamron is really good value for money based on its price.