Originally posted by Giklab The DA is 4.5 up to around 200mm I think, while the Sigma drops to 6.3 pretty early.
At 135mm, the Sigma is 5.6. I'm not sure that's an issue for buying or not buying the lens. For Aperture, both are slow, let's not quibble about how slow. For me the big difference is the Sigma covers 18-55. That avoids a lot of lens changes. Not covering 250-300 is a much smaller difference than 18-55. Many of us use the DA*60-250 instead of the DA*300 because the difference is so small.
So it really depends on intended use, whether you have something better, and whether you want WR, which is available on the 55-300. If what I have now is the 18-55, and I'm looking for a walk around lens, my advice would be get the 18-250 and avoid the lens changes.
If you own the DA*16-50, Sigma 16-50, Tamron 17-50, or any other good lens in the 16-50 range, then the 55-300 makes more sense, since you'd be taking the Sigma 18-250 off the camera in favour of one of those lenses when you had the Sigma on, in any case.
After I bought my Sigma 70-300, DA*60-250, and A-400, my wife bought a Sigma 18-250, just for the convenience factor. Especially for many family events etc. you just want few images with minimum fuss.