The latest figures from AEA show that when choosing to fly to/from the Nordic countries you most likely to be on time.
These numbers reflect the number of delays (more than 15 min) in the periode of April-June:
Helsinki - HEL 12,0 %
Oslo - OSL 12,4 %
København - CPH 13,7 %
Stockholm - ARN 13,8 %
Helsinki (Finland) has the best figures in Europe followed by Oslo (Norway).