Winter is best.
• Winter has snow
• Winter has no pollen allergies (though sadly there are indoor allergies)
• Winter is cold and refreshing compared to the rest of the year
• Anything you can do in other seasons, you can do in winter. Don't mention swimming, because you can do that indoors
• When it's freezing, you can keep piling on more layers
Summer is worst.
• Humidity and nausea
• Annoying marketing and advertising
• Boredom
• Expensive electricity due to fan / air conditioning
• When it's hot, you can't rip off your skin, and cooling has its limits