Like a couple of the others, I'm able to comfortably hike year-round where I live. Our changes in seasons are pretty subtle around here: summer is reliably warm and sunny while winter is mostly warm and sunny! Nonetheless, I think late fall into early winter (Nov-Jan) is probably my favorite time of year to hike in my local backcountry.
By then, temps are a little cooler, most of the nuisance critters are hiding for the winter, water starts to become more reliable and what small changes we have in the leaves are underway.
Aside from the infrequent and mostly short-lived rain or snow, our late fall and early winters are blessed with cool clear days and frosty, but clear nights. I especially love the crisp bite to the air on a clear fall morning. I look forward to waking up to the first day of that weather each year.