The reason why 16mm and 10mm are not as popular is because they are much newer, and pretty much everyone that wanted a third party ultrawide already got a 14mm. And I think the 16m and 10mm are crop sensor only, while the 14mm is also for film and full frame.
All of these are great lenses with ultra wide field of view and fast aperture, sharp optics. Only problems are QC: decentering and distance scales miscalibration. So when you buy one, get it with warranty and do some tests. My Samyang 14mm for example isn't as sharp on the left half of the frame. This becomes noticeable with astrophotography because stars on the left half turn into lines instead of perfectly sharp dots. And its the second copy of the 14mm, the first one was worse. You can test the distance scales and simply memorize where "infinity" actually is, in case the infinity sign is wrong. There are also instructions how to fix this yourself, its not too difficult.
Though, to be fair to Samyang, decentering is often a problem with ultrawide lenses, of any brand, because the optics must be so precise and even a small error will become optically visible.
Edit: I have the 14mm, but if I was buying today, I would get the 16mm. Its not as awkwardly wide and not as heavy, has detachable hood and takes filters, probably easier to focus,..
My attempt at astro (in a city lol, press M to see bigger size, I swear there are some stars):
http://500px.com/photo/50888178
But its also good for indoor photography:
http://500px.com/photo/68369283