I have the 1.4 and rented the 1.2 from Vistek last weekend. As far as sharpness goes, in my opinion, it was a toss up between the two.
The 1.2, however, like others have said, has much better contrast and the bokeh is just incredible. If you think the 1.4's bokeh is something to brag about, the 1.2 will rock your world.
The downside is the price. I don't think I can justify the price difference for something that only myself and fellow camera enthusiasts would ever notice, and even then the difference isn't THAT big.
The extra durability and weather sealing is definitely a plus. If you think you need the durability and sealing with your work in the future, then perhaps the 1.2 is the best choice for you.