The main wind direction is southwest, resulting in a temperate maritime climate with cool summers and mild winters, especially in the west of the country, on the North Sea coast, the climate is more Atlantic influenced (mild winters, cool summers) to the east, the Atlantic influence is slightly lower, so it's more a subatlantic climate near the German border with slightly colder winters (mild to moderate-cold) and slightly warmer summers. (Source Wikipedia)
Best time to travel: basically, any time is suitable to visit the Netherlands. However, you should prepare for stormy and changeable weather. Only in summer there are some sunny days. The rainfall is evenly distributed over the year, in the spring there are short, heavy downpours.