I previously used the Sigma 10-20mm (early version) and switched to the Pentax 12-24mm. The Pentax is sharper and I usually shoot at 12 - 14mm for interiors. When shooting at 10mm, the Sigma had a tendency to elongate furniture in close/smaller rooms and was unacceptable and uncorrectable. I believe the new Sigma is very good, but haven't tried it. Both lenses will produce distortion in some situations (correctable with K7 in camera setting or photoshop). I did use a fisheye when the client wanted a virtual tour, but it was a nikon with the IPIX system (IPIX was the easiest/best at creating virtual tours as it was a 2 shot system and the software did all the stitching and correction work automatically). Re your shots, if you are happy with them then the fisheye is fine. I doubt you will get a realestate company to buy or use them for sales purposes (unless the distortion is corrected). With the fisheye and correction software you are in business... just takes a bit more post processing.
Last edited by ivoire; 01-17-2010 at 05:17 PM.