prustyaditya wrote in post #14808200
Ive heard they are both good lenses, but according to most comparisons and reviews online, The canon MKI (and MKII for that matter) are much sharper. The only thing that the Sigma has over the Canon lens is OS, which may be useful to you depending on what you shoot.
You're reading the wrong reviews. Those are for the old versions of the sigma. And even then, I've used both the older HSM II version of the sigma and the canon MKI and couldn't really see much of a difference in IQ. The new OS version is sharper than the MkI canon, but most reviews compare it to the MkII, thus making it look not as good as it should be (after all, its being compared against a lens almost twice the price). In fact, the sigma OS is considered by most who have used it to be second only to the canon MkII in IQ, and that is saying a lot.
The sigma would be my choice over the canon MkI because you can get it new vs second hand, and you get better IQ and better OS, though the canon will have slightly faster focus and has nicer build.