Regardless of the make just be prepared to have to have your lens calibrated - especially if you can't adjust af in your camera .
I love my new sigma 17-50 2.8 is. I was prepared to need calibration but I was good out of the box .
What does it mean to calibrate a lens, anyone? Seems like something important I should know if I want to extend the longevity of my gear.(you will be popular with the 40mm lens)
Ha ha ha, woo! I think the pancake looks so silly. I'm excited to get my shotgun mic/shoulder mount in the mail this week. Last two things on my list (for now): battery grip + polarizer.
The af or auto focus can be calibrated to optimize or better match your lens focus to your camera. It doesn't really affect the longevity.