Originally posted by Pix I found some models like: -Pentax DA 21mm f/3.2 AL Limited -Samyang 16mm f2.0 -Tokina 17mm f3.5 -Pentax da 15mm f4 (more expensive)
I had a similar dillema some years ago, but fewer choices. I started with the Samyang 14mm, because at the time it was far cheaper than the others and the 16mm f2 was not yet released. Later I got M 28mm and then DA 21mm ltd. Oh and DA 35mm, which is not really wide on APSC, but a good affordable prime.
The DA 21mm is amazing, really great. But it is not ultra wide. My recommendation is go with DA 21mm if you want a lens that is wide, has great colours and contrasts and is super compact. Get Samyang 16mm f2 if you want something really wide and fast. Samyang 14mm is almost awkwardly wide and it has some other weaknesses (cannot remove hood, cannot use filter, had decentering problems in the past, really difficult to focus due to wide DoF). Sharpness is not too different, as all three of these lenses are very sharp.