Re: which swarm cells to destroy?
Boy am I confused! I thought the question was which cell should you keep. The answer was both of them. The question would indicate that you were already resigned to letting the hive swarm. If you want to prevent the swarm, the quickest way is to pull the queen and a frame or two of brood and move them into nuc or empty hive. Put the new hive where the original one was and move the old hive across the yard. This is a flyback split or artificial swarm and should take care of the swarming instinct for this year.
Thankfully, the bees are smarter than I am. They are doing well, in spite of my efforts to help them.