From the reviews I've seen, the Sigma 10-20mm is probably slightly sharper than the Tamron/Sony 11-18mm.I would say either Tamron/Sony/Konica Minolta 11-18mm or Sigma 10-20mm F4-5.6
But which one is the sharpest, I cannot say as I dont own all of them
But would like to know either Sony or Sigma is sharper?
Kevin