Spring. Partly due to being born on May day, the 1st. It is, in Pennsylvania, where I live, a time of green and fresh air after good rain. Flowers everywhere and life returns after the cold, ice and snow.
You get to be outdoors more, it isn't hot like summer, perfect sleeping weather - chilly but not cold at night - when you are out on a spring day and the sun shines, the warmth penetrates without beating down on you. Like Hilander said, no ticks, no mosquitoes and the wasps might be around but they aren't the dicks they turn into in September.