Very hard to answer this question since it depends on what I'm shooting, but if it came to the crunch, it would be a flat out tie between the 14-24 and the 85 1.4G. These 2 are staples in any bag.
But then, there are still others I love like my outstanding 28mm f2 ais and the woefully underrated Sigma 50mm f1.4 (I have a lovely copy)...some of my favourite shots have been taken with these lenses too this is a hard choice!!!