Originally posted by rogerstg Except the OP does not have that lens to consider selling.
FWIW, since my wife now shoots Pentax DSLR, I have both the Sigma 10-20 and the DA 12-24. I recently bought the 12-24 and am glad that I did and prefer it's versatility. Not really relevant to the OP though.
Yep, I've got both now as well, having had the DA 12-24mm for many years, and the versatility aspect is different between them- meaning either at the longer or the wider end. I love going super-wide with the Sigma, and sometimes appreciate its extra half stop in low light.
20mm on APS-C is pretty versatile (think DA 21mm Limited), but as a 24mm lens, the DA 12-24mm is indeed good as a walk-around general purpose focal length to be sure, as would a 35mm wide/normal on a FF body, then you can go wider angle as needed.