Dear All, I am planning to buy a good portrait lens for my crop sensor camera, EF-S 17-55, Sigma 17-50, Tamron 17-50... I have heard/read equal good and bad things about Sigma and Tamron. Therefore, I get inclined to Canon. Has anyone used Sigma and Tamron 17-50 mm with Image Stabilization. If yes, please share your experience. Regards, Gurpreet.