I picked winter, the atmosphere of it with all the good cheer, snow is purdy too.
I struggled to pick just one though, I really like living places that have clear seasons not just a gentle minor temperature difference as the year goes on, I so couldn't live near the equator
i prefer: late spring, really early summer and really late summer, this is largely down to the fact of medical conditions xD
although i do like auumn(fall) when the leaves are changing and winter when it snows or theres a light frost on the ground but i usualy have to enjoy that from indoors =[
Winter. No humidity, so you're not all sticky and sweaty. That alone puts me in a great mood when it's cold. Christmas, New Years, tax returns! Yes please.