Sir both are really nice colors
SILVER is
1) Easy to maintain
2) scratches and swirls not visible that easily even after 2 years of use ( telling this from past experience as i had Altis Cruisetronic in medium silver back in 2011 )
3) Better Color than Gun Metallic for modifications , esp if you are planning to get your car Bodykitted then white and silver both are best colors for Decent Modification
4) Car looks slightly bigger due to the light shade
GUN METALLIC
If you plan to keep your car simple and dont have any plan for body kit and such stuff then Gun Metallic is the best Color , looks really really nice and Graceful , if you compare a stock Corolla 11th gen in Medium Silver and Gun Metallic , i will choose a Gun Metallic
However its difficult to maintain
Gets dust n dirt very easily and in much lesser time than lighter shades
Scratches are easily visible
The car gets swirls within first 6 months with Black the case is even worse as you get the swirls within 1st week after getting the car ( if you dont have 30 mins daily to pamper it yourself if your driver cleaner who ever cleans it then swirls will come really soon )
Gun metallic looks really really attractive and graceful if properly cleaned and waxed every weekend
Considering whatever i said
SILVER is better
However if you can maintain a gun metallic or Black then nothing can beat dark colors
Hope tht helps
Best of Luck in choosing
