I'm with Baz on the warehouse express thing..i have bought all my lenses and my latest camera from them,when you ring whoever you get they are really helpful and i've not spoken to one yet who does'nt know what they're talking about and next day delivery.....
As for the quality issue i had the nikon 18mm-70mm kit lens and now i have the sigma 18mm-200mm which stays on the camera,obviously i'm not a pro but i can't say i've noticed any discernable difference in quality of the images....
