If you look here:
http://www.the-digital-picture.com/Reviews/Samyang-24mm-f-3.5-Tilt-Shift-Lens-Review.aspx
there is a vast difference in quality in the lenses with the Samyang being noticeably less sharp than the Canon virtually all through the exposure range which would really impact on any architectural shots.
But the bad news is that the Canon TS E Tilt-shift lens is over twice the price of the Samyang.
You might be able to use the Samyang from f8 onwards with sharpening but personally I would definitely go with the Canon model if affordable or simply wait until I could afford it and use software to correct the leaning verticals etc.
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