North East India is an incredibly vast place, and the best time to visit is never really particular. For enjoying the seven sisters and waterfalls, you might want to be there in monsoons; because the lush greenery and rains are a view to watch! You can also visit Arunachal Pradesh during September or in December to explore the calmness of Buddhist monasteries, snow, swift streams and beautifully cloudy peaks that will make you awestruck.
During the last week of November and the first week of December; there are many festivals in Manipur, Arunachal Pradesh, and Nagaland; that is sure to grab your attention and keep you entertained. The weather in the northeast region is always unpredictable. There is endless rain in some parts which make them pleasant and bring in cold at the same time.
However, if you are still hunting for the best time to visit; then it should be both the monsoons and winters. During the monsoons, there are glistening waterfalls and lush green surrounding that are a treat to the eyes. While in the winters there is sparkling snow that covers the entire area like a sheet. However, there are a lot of landslides during the months of monsoons, making it a bit of risk to travel on the roads of this area. However, at the end of the day, it is your choice as to what season you want to choose for visiting this pleasant place.