sigma is coming out with 17-50 OS HSM. maybe you can wait out abit before deciding? unless you need in a hurry haha. i am using the non vc one. am pleased over the outperformance i got compared to the kit lens.
silent AF is something really good, but even AF is loud, it doesn't cause any damages on the image you taken right?
anyway, VC or non-VC, both are sharp and good lens. i'll look forward to tamron releases a new 17-50 with USD =)