The season that is most frequented by visitors is between April to September when the country doesn't receive rainfall and you can go around all the tourist attractions easily. But if you ask me, I would suggest go between October to March if you want to avoid crowd. Sure, you might encounter some rains and a bit of bad weather during your trip, but you will definitely enjoy the pristine beauty of the country when there are less tourists around. If weather does not bother you, this is the time for you! Also, the rates of accommodation, food and commuting are far less in the off season.