Answer is 304. I highly recommend 304 grade of steel in steel railing. Because 304 grade always have more resistance from water/ rain hence more life, in 304 the length of steel also high so result weight & strangeness of steel pillar is also high. so everything works GREAT with 304.

I highly recommend to use & test this 304 originality before apply. sometime shopkeeper emphasis on 202 in order to save their cost & increase margin. The only disadvantage of 304 is price. price of 304 is some high compare to 202. Although more then 70% railing uses 202 quality in domestic.But again by ending this blog its your choice that you have to choose whatever you like.