There is not only the best season/time to trek to Everest region; there are two best times of the year: Spring ( Mar-May) and Autumn( Sept. Nov). Frankly telling, if you can tolerate crowd, you can trek in Everest Region in Autumn and if you want to avoid it, you are suggested to trek in Spring. But, both seasons/timings offer you the finest and the rewarding views of the mountain summits and the weather condition will absolutely be fine with no rainfall and snowfall.