depends on your uses. if you are doing a paid job, need to do large prints and thus needs a lens that can provide you the ultimate performance and optics (less the slower AF of Canon 85L due to the large and heavy glass), go for Canon 85L. If not, get a copy of Sigma 85mm. It cost about 40-45% of 85L, but gives you very similar results.
I'm probably going to buy the Sigma 85mm if I intend to get a 85mm prime lens. The cost savings could be used to buy another Canon L lens that is superior of it's class (without much or even competition), like 16-35L for UWA or 70-200L f/2.8 II for telephoto zoom.
i will go for 16-35 and lastly 70-200 F4 IS as i think F2.8 mk2 is too heavy to travely around