I don't know that I have a preference on season from a climate standpoint.
For me:
Spring pros: Virgo,
Coma Berenices, Leo, Ursa Major, and galaxies. Of course, galaxies are all over the place all year long, but in northern spring the volume ramps up a lot. The frog songs down at the pond provide a nice chorus to the observing. Nice to be able to shed some layers of clothing as temps warm.
Sping cons: I live in tornado alley. 'Nuff said. I'm lucky if I actually get a clear night not wrecked by thunderstorms or mired in cloud cover. Around here, observing or
AP are lean in the spring.
Summer pros: Looking inward toward the galactic core (Milky Way), loads of nice nebulae, globular and open clusters. Warm nights and t-shirt weather. The fireflies are fun to watch too.
Summer cons: Full dark arrives quite late and don't get me started on daylight saving time. This cuts down on how late I am willing to stay out on a work night. For
AP, harder to cool the cam down properly. The worst scourge of summertime astronomy, in my mind, are the mosquitos! And around here, the swamp-butt humidity gets old pretty quickly. I usually find myself longing for winter observing.
Autumn pros: Just something about autumn. Cooler air, crickets, Andromeda! Some good meteor showers. The mosquitos have backed off. Another especially good time for galaxy observing.
Autumn cons: Dew! Dew! Dew! Around here, the temperature and the dew point are often walking hand-in-hand. Everything is wet and adrip. And the spiders! Last year's babies have ripened into large hairy brutes that sit on your eyepiece, sit on your atlas, sit in your bag of
AP cables, ride around on the back of your shirt. The new crop of babies are busy ballooning and stringing web all over the place, including your face and telescope. High heebie-jeebie factor.
Winter pros: Somehow it just feels more secure being all bundled up warmly. Orion! Air masses can be drier and kick the dew point down. More good galaxy hunting. Outer bands of the Milky Way, nebulae and open clusters. Easy to cool the cam down and low noise for
AP. It gets dark really early!
Winter cons: Its #$%^@#$ cold out there! Dew freezes! I can tolerate it being pretty cold, but when you get a slight push of a breeze it can be a game-changer. Sometimes it gets old setting up in the dark. I often find myself longing for summertime observing.
Other factors...
Northern summertime and even into autumn tends to be the time that wildfire season is in full swing, at least in North America. All that smoke gets into the upper atmosphere and can really bog down the transparency of the atmosphere. Of course, I'd much rather be complaining about the transparency than suffering from a wildfire...
As for seeing conditions (turbulence in the atmosphere), this is largely governed by weather patterns and position of the jet stream, frontal boundaries, storms passing (or just having passed). High-pressure anti-cyclonic systems seem to steady things up a might, while low-pressure cyclonic systems muck it up. I've not really logged data on that, though, and am foolishly relying on memory.
Just my thoughts...