Autumn. No bugs, no bright sun, grey skies, not too cold and not too warm, good chances of rain and thunderstorms.
I've never been able to decide this. I love them all for different reasons, and every time a new season starts, I say it's my favorite. I like spring because of how bright and vibrant everything is. Also love the temps. I like summer because of the activities: swimming, barbeques, and driving with the windows down on warm nights. But I hate the heat and humidity. I like fall because of the colors and the smells. I like winter because of the snow, the silence, and the cold. I love to bundle up, sit on my porch, drink coffee, and enjoy the silence snow brings. I can never choose.
I live in a town near Portland, OR, and early spring is my favorite season here. (A few weeks ago it was perfect, basically.) Primarily for all the flowering trees. Cherry blossoms, magnolias, dogwoods, etc. You see pretty much every shade of pink, and it beautifully complements the light green budding leaves of the non-flowering trees. It's a vibrant and soothing scene. Especially right after a light rain, when the air is cool and crisp and the clouds are clearing up. I used to live in the Los Angeles area, where the seasons are basically summer, summer, summer, and a short rainy season. My favorite was the short rainy season (a.k.a. "winter") because it was a relief from the constant heat and sunshine. I can't imagine how I would fare in an actual desert.
17° C is the upper end of what I think is the perfect outdoor temperature range. Indoors, though, anything lower than 23° C is uncomfortably cold. Except when coming in from the heat.
HAHA where I live is hotter than that and it's not even a desert! 'Cause I'm so tough (Actually a wuss).
I like autumn, to watch the leaves change and the weather is mild. At least I would if there were real trees around here, and not evergreens that look like something out of nuclear disaster.