Personally, unless there is an obvious cause, I always locate the puncture site on the tube to ensure the offending cause is located and removed.
Then replace with a spare.
As I get to a suitable point (work if commuting, lunch if on tour) repair the p*ncture.
As I have said before - it is a great ice-breaker. I have spent many a happy how talking to other cyclists whilst repairing a p*ncture