I always choose to travel in the fall. It is usually cheaper wherever I want to go and, since I have no kids, I don't have to worry about a school schedule to work around. Of course, if you have little ones, you can often work with the teacher and school to take all the required reading and homework with you to keep up. If you can take advantage of not traveling during the most expensive times of year (summer and holidays like Thanksgiving and Christmas), you can really save big bucks. In particular on airfare. Fall is one of the best times to go to Europe. Airfare can easily be halved at that time. With all the kids in school, it ensures that crowds during the week will be much smaller and allow you to do and see more while at your destination. This infographic shows the different travel seasons in the U.S. The same principles can be applied to other destinations around the world.
What's been your best experience traveling during off-season or shoulder season?