I've bought from OSD before because they were the cheapest I could find. The only problem is that with them is that because they are based in Hong Kong, if you have a problem with the lens once it is delivered then you have an expensive postage bill to return the lens.
I have a Sigma 30mm f1.4 and I absolutely love it. It's by far the best and sharpest lens I have but I've heard a few stories of people buying soft copies that they've hd to return several times before they get a good one they are happy with.