Each season has its own merits and demerits. if you are looking for moody style images theb rainy season, if you are looking for vibrance then then time after raony season when the skies are all clear and clean all the way till winter. if you want specific genre's like astro then december to may is preferred. It all depends on which place are you at and what is it that you wish to capture. A place like Kashmir in winters looks different gives a different vibe while if you visit during autumn, it gives you a different vibe. So there's no perfect season as such. It is all about what do you want to capture.