Autumn.
Winter is super cold and there's snow everywhere. Ew.
Spring is still cold, albeit better. But, it still has some snow, and everything's melting, so there's mud everywhere and water everywhere, and it's just wet in general everywhere. And still not warm enough that you can go outside without a coat.
Summer is bleh, far too hot and humid.
But Autumn, Autumn is perfect. It's still a bit chilly but warmer, and you don't have all the snow melting and making everything super wet and disgusting. And you have all the trees that change colors and it's awesome, and it smells good.