I haven't used those three, but I have used the Zeiss 50/2.0MP, brilliant and the Canon 50/1.2, brilliant these are the best at that length, if I had to choose from those selected I would go for the Sigma 50mm. And then if Canon release a 50/1.4 mk2, I would buy that.
But all of the above lenses produce better images than an unreleased lens.