Yes bro. The tamron is a bit sharper than the sigma. But dili kaayo na mumatter especially if you get a very good copy of the sigma. Though the tamron has a larger max apperture @ 2.8 throughout its focal range, sigma has the optical stabilizer for low-light. Both lenses need to be stepped down a bit to obtain its sharpest image (for sigma's case its @ f5.6 for both 17mm and 70mm). Also sigma has a better AF motor (HSM is silent and fast) than tamron. Both have good bokeh but I prefer sigma on this one. For contrast, some say that tamron has a tendency to over-contrast(maybe it depends on their copy).
For me it really depends on your preference. If you want a faster lens and think that the 17-50mm range is enough for you, go with the tamron. But if you want an optical stabilized lens with a longer range and macro capability, then go with the sigma.
IMHO, you can't go wrong with either one as long as you get a good copy.