I voted for the 50 cuz im using a 35mm on my APS-C so thats roughly a 50mm Fullframe. Id love to use a 35 on my aps-c but i dont find any appealing 20mm lenses.
Why not the Zeiss 21?
Because i want to have a wide open aperture and that gets less and less realistic considering i need a ca. 20mm lens for my APS-C. Plus the Zeiss is really expensive to me!!
Next thing i will buy is the Samyang 35mm 1.4. Im used to manual focus anyway with my tons of m42 lenses even without manual focus screen through my viewfinder My eyes are still fine ^^
At the moment using zeiss 35mm 2.8 Zebra a lot