I have been using 5s 16GB from more than 1 year. Currently running on latest version of iOS. i.e. iOS 9.2, without any lag.
After this update this phone will show 12 GB available. For this reason only I would say, you go for 32 GB or Higher Variant.
Apart from storage the phone has no issues so far. The OS experience is far better than other OS available in market.
Asphalt 8: Airborne runs like butter, without any noticeable lag.
This 8 mega pixel camera is far better than any other INR15-20k 13mp camera smart phones available in market.