The Sigma is one hell of a lense but get's partly beaten by the Samyang 35mm 1.4, especially in the corners. It's sometimes interesting to see how other good competitors are getting less known if someone hypes the new one
If you're willing to pay some attention on the pictures and you're not afraid of manual focus (but therefor with a fantastic focus-ring), you can get the samyang for a fraction of the price.
Just a link, not a picture (it's not that important, but anyway): http://tf.weimarnetz.de/downloads/35mm_compared.png
pictures (c) by photozone, just taken for comparision
If you have a great photo, you are not really going to "see." A difference between the Sam Yang and the Sigma. Me..I will take my Sigma and the AF every time. It a way more capable lens for more types of photography.