20-50mm or 16-50mm lens

I`ve got both lenses , a top copy of the 20-50 and I`m sure a very good copy of the 16-50 (because it is not decentered)

the 20-50 is perfect everywhere at 20mm even wideopen for sharpness, there`s minimal CA too , it betters the 20mm prime by a margin both lenses at F3.5 and is as sharp as the prime !

the 16-50 needs to be stopped down to F5.6 to be good, it`s pretty soft all around the edges (top and bottom as well as sides) wideopen and the lens never gets as sharp as the 20-50 does too even at F5.6

at 50mm both lenses suck big time, very soft if shot further than garden distance .. at infinity , they`re that bad that I`m sure with an NX500 you`d not lose anything shooting at 16mm / 20mm and cropping and upsizing !! . I`d say class these as 16/20mm primes which zoom if absolutely desperate or doing closeups

I have used drastically decentered samples of both , sadly Samsung seem as bad as Sony for sample variation .

Build is a sure fire win to the 16-50, the 20-50 feels like its going to fall to bits and I`m sure mine is on the verge of just that, I`ve had it since the NX200 days as it`s a top sample so has been hammered , also its a pain having to "open" it before using it - the 16-50 extends on switch on and the electric zoom, on the ring is just fine . the 20-50 not having OIS isn`t a biggie, the OIS on the 16-50 seems pretty useless anyway (as it is on the Sony 16-50) , it`s nothing like the OIS in Panasonic kit lenses by any stretch .,