As for high season standouts, mainland Europe has two: Czech Republic and Switzerland, both of which boast a six-month period of peak travel. Similarly, Bolivia has the longest high season in South America, running May through October. The United States is fairly average, with a three month high season (June through August), a five month low season (November through March), and a four month cusp period (April, May, September, and October).
While there's no guarantee consulting this map will save you any dough on flights or accommodations, it should definitely help steer your decision making. Then again, you could always just hold out for some crazy-cheap flight deals to come around.
h/t Matador Network