I voted for the Sigma, but that is not really my choice. I have the Sigma 150mm 2.8 Macro lens. For $700 ish you get good glass, longer than 100mm which gives you more working distance and smoother background blur, and still the 2.8 open aperture. The 180mm offerings cost you 2/3 of a stop which sometimes is a big deal. This lens has worked excellently for me. I was on a budget constraint which is why I didn't get the 180mm canon, and I didn't want the shorter working distance of the 100mm. (the L didn't exist at the time and wasn't a consideration)


So that's my two pence!