I've owned both, I now own only the Sigma, sold the Samyang. Mine was among those with very large error between the focus scale and the actual focus distance, and I could not get a distant corner sharp no matter where I focused- I suspect that improper flange distance plays hob with the floating element internal focus aspect of my Samyang...anyway. Neither was/is my favorite lens and I rarely use 14mm, but for me I preferred the Sigma, and since the request was for AF, I'm comfortable recommending it in this context.
PS- it's pregnant horse distortion.
