Sorry guys but your both wrong...and kind of right.
The P-51 served in Korea until the Jets came out as did the Corsair.
The Corsair had the longest production run or any piston fighter ever produced. However it didn't see much service with any country after 1969. The Mustang was used into the 80s. I imagine this was largely due to parts and the total number or both aircraft produced.
Not saying one is better than the other. They are both awesome aircraft.
Question on the Corsair: Can anyone tell me 4 advantages to gull wing on the Corsair?