Hi everyone, I've had my kit lens (18-55mm) for 6 months now and I think its time for an upgrade. I have been looking long and hard into a replacement from the Canon 17-40mm f4L, Sigma 18-50mm f2.8, and the Tamron 17-50mm f2.8. I think due to the crop factor I should stick with the later 2 as I can't see myself upgrading to a full frame sensor for quite some time and would definitely get more use out of the wider angle and f2.8 aperture. I've read the Tamron is sharper through out the range at f2.8 so at the moment I'm leaning towards that. I've also heard bad things about the quality control with both the Tamron and the Sigma lenses, would I be dicing with death going for a second hand version of either of these lenses?! Anyone got any advice on these lenses or any others I should be considering? Thanks in advance Sorry if wrong box.