Do you have any experience with Samyang 14mm? Some reviews say this lens is good except for distortion. Is that's possible to correct the distortion from lightroom? By the way some people on Amazon report the lens will get dust easily, how is the build quality of this lens?
I haven't used the Samyang 14mm, only the 35mm.
The IQ is excellent, and the build quality is not us to zeiss/takumar standards, but it's good enough (mine was bought second-hand after a fall, the bits that broke were small bits of plastic, they'd survive normal use but not a fall). With the 35mm, dust could get inside the mechanism, but not between the elements, can't comment on the 14 in that respect.
With regards to the 14mm, from all reports it even beats the Canon L at some settings. But because of the barrel distortion (like 5% or so), resolution is really high in the centre. I'm sure you could de-barrel it, even manually (take a test shot of a brick wall or print a grid and save the numbers you use to get it square), then centre res would be a bit less. Still, at 1/4 the price of the L, it can't be beaten for the money...