At first glance, it might seem like the best time to go on vacation is when you can get the best prices. However, even if you're retired and are free to travel whenever you want, price should never be your only consideration when planning a trip.
If you insist on going to a popular destination at a popular time, your best bet is to plan for crowds and take steps to avoid them. Wake up extra early so that you’re near the front of the line for the first attraction of the day. Don’t eat lunch or dinner at peak dining hours. Take a break during the busiest part of the day and extend your sightseeing right up until closing time, when some people will have already tired themselves out and returned to their hotels. Call ahead to find out when large tour groups will be visiting any museums you want to see and plan to avoid those times. Get a tour book that will advise you on potential problems like free admission days that make an attraction extra busy so you don’t get caught in an unexpected crowd.
Learn more about how seasonal considerations, school schedules and work schedules should factor into your vacation plans in my Financial Edge article for Investopedia, The Best Times to Take a Vacation.