Im looking at the Sigma 10-20mm F4-5.6 EX DC HSM or Tamron SP AF 10-24mm f/3.5-4.5 Di II LD Aspherical (IF) for my first wide angle lens. Which do you think is a better choice? Or is there another better one out there other than these two? Please help me decide. I dont want to regret my purchase. Thanks