I live in Wisconsin and commute everyday, so weather is a big factor in the pleasure and safety of my commute. That is, I don't choose certain days to take the car instead of bike. I bike no matter what the weather. Instead of choosing to take the car or the bike, I chose which bike to take. If it is snowing, it is a fat-knobby-tired mountain bike. If the weather is nice, it is a zippy lightweight. If it is slushy, it is a reconditioned junker.
My favorite season is fall because the air is crisp, the colors are beautiful,the roads are generally dry, and the days are still generally long.
My least favorite is spring because it rains so frequently and the rains are cold, and the shadow of winter darkness still has me riding in night-like conditions.
I also like winter because the weather is predictable. I would rather be in snow that in rain. Biking in snow is an absolute scream. I like biking up to cars that are stuck and helping people out. Once the snow gets as high as the crank-case, then it gets too difficult to bike effectively, but it is still fun.