The best time to visit Cambodia is pretty much anytime! Heat lovers rejoice! Because of its tropical location, Cambodia is hot and humid all year round, with an average temperature of around 30°C.
The hottest time of year is March-April when the temperature can rise to a stifling 40°C. This is followed by a rainy season which runs from May to October. During the rainy season prices are cheaper and everywhere is less crowded, however it does rain a lot, especially on the coast. If you are trying to find the best time for you to visit Cambodia for the weather, it is not worth planning a trip to the beach during the rainy season.
The most pleasant time to visit Cambodia is during the dry, cool(er) period between November and February.