There isn't really a best time of year, but there might be a best time for you. Some like to schedule a session based on their seasonal preference in clothing and/or type of location. Others give greater consideration to weather and want to avoid the heat of summer or the cold of winter.
Keep in mind that we normally shoot on weekdays and in the late afternoon/early evening. Family sessions start about 1.5 hours before sunset, and senior sessions about 3 to 3.5 hours before sunset. From late Fall through early Spring, early sunsets necessitate earlier sessions. This could require students to leave school or parents to leave work early. Seniors should also plan ahead if they are involved in after-school activities that might make scheduling more difficult. In these cases, a summer session might be the better choice.