The Tokina AT-X 116 PRO DX-II is F2.8, so wouldn't this be the best option? Unless you really need the extra 1mm width?
Found this interesting comparison:
http://www.kenrockwell.com/tech/digital-wide-zooms/chart.htm
Stated the Sigma 10-20mm has 'sloppy' mechanics, whilst Canon & Tokina...