My favorite month in interior Alaska is March. The days are getting long (spring equinox is in mid-March) and are typically brilliantly sunny with sparkling white snow. The sun even has real WARMTH in it again, whereas in midwinter the sun is merely ornamental. Even though we’re having a little colder than normal weather these first few days of March, with overnight temps down to -35 F, it’s been lovely and above zero in the afternoons. We have over 2 feet of fresh snow that all arrived in the last week of February, so we’re set for a lovely month of snow sports: cross-country skiing and skijoring are the ones I enjoy; others do snowboarding, downhill skiing, dog mushing, and ride snowmobiles (which we call “snowmachines”). The warmer, longer days perk all of us northerners up – we all seem to have more energy and want to expend more of it outside to enjoy the warmer, longer days. March is a month of spectacular ice sculptures (the World Ice Art Championships; see http://www.icealaska.com/ ), dogsled races, and lots of sparkling sunshine. It’s the month when it occurs to me that I ought to put sunscreen on my face.
Can I use part of two different months? Here in upstate NY, I love late April, early May. After a long hard winter, the coming alive of the world is just gorgeous. The growing sunlight filtering through pale green new foliage gets my blood flowing every time and walking about looking at all the new shoots coming up from the ground is an adventure every year. Even weeds seem like old friends long gone.
I have to think about it, because I don’t think it’s right now. It might be a toss up between May and October. May brings brightness and a mood boost, and October is crisp and nice-smelling.
My favorite times span months at a time here in Virginia. What I don’t like are June, July, and August unless we are back in Wisconsin where temperatures are normally more humane.
Right now the robins are singing loudly every morning along with the cardinals, towhees, white-throated sparrows. The bloodroots and gingers are blooming, the spring beauties can’t be far behind. Henbit which is a noxious, non-native, invasive weed is in full pinkish purple bloom covering the fallow farm fields in their billions. I still love to sit down on the edge of a field and look at a flower or two with my 10X loupe. They’re really quite exquisite. There is also a steady contented sounding buzzing hum in the background as the bees work the flowers. Soon the tundra swans and the sandhill cranes will fly over during the night on their way back north. They can make a bit of a racket so we sleep with the windows open in the hopes of catching a glimpse, if there is a good moon it’ll be spectacular. Other than that it’s pretty much the same old same old.
Here in Northern Illinois I’d vote for October. I like all four seasons, but autumn is colorful with the bluest skies. And the cool air feels good after a typical Midwestern summer, too 
The only way you’d catch me in Northern Illinois would be if I was a Wisconsin State Senator. 
Here on the Central Coast of California, I like summer best. It gets hot up here in the mountains, especially in July, but it’s a dry heat, and I don’t mind it (and if it really bothers me, I’m only 15 minutes from the beach). I love the long days and the predictably sunny, warm days.
If I have to pick a particular summer month, I’d say June. By June, we’ve pretty much dried out from the winter rains, but fire isn’t (usually) too much of a worry yet…and there’s a whole lovely warm summer stretching out in front of me.
Redwolf
October. I can drive around with my window down.
Trees look extra nice. Ren Faire and music festival
season starts.
South of England: I love May and September the best. Life burst forth everywhere in May, there’s bird babies and the garden is at its best, and one of my favourite things in the whole world happens: apple blossom. There’s no place I’d rather be in May than right here.
September, you get the last shreds of summer warmth, the crisp mornings, the glorious colours, smell of woodsmoke.
I too can’t decide between May and October.
May is fresh and invigorating with the prospect of summer ahead after the long climb out of the winter.
October has great colours and crisp mornings but for me it has a melancholy feel as we drift towards the cold dark winter months.
I’ll echo that. Although I have a soft spot for the Bonzo’s song “How nice to be in April, now that England’s here.” (Yes, it is that way around.)
Harking back to Norn Iron, I think may favourite month there has to be August - if you can spend it outside. I think that goes for Scotland, too. The worst of the midges are gone by then.
“The only way you’d catch me in Northern Illinois would be if I was a Wisconsin State Senator…”
…and they’re welcome here as long as they’d like to stay!
September, I think…yes: every September I tell people how I wish that was the perpetual local climate.
In Maryland it’s mid-Spring, maybe April. When the daffs, cherries/pears/dogwoods are blooming thru when the azaleas bloom.
In New England, October, when the leaves are turning.
I’m a sucker for riots of color.
October. Anyone in New England who says otherwise is lying or planning a move to Florida.
September
This year it looks likes it’s going to be March. Early spring flowers are already blooming and the trees are budding. But it’s when everything pops and the countless shades of green have replaced the grey and brown of the mountains. And I’ll get to go canoeing if I’m lucky. If not April.
I say it’s probably a toss-up between May and October. They’re both at about the right temperature, plenty of time (and reason) to go outside. Although, living with the AuSable River right in my backyard, it looks beautiful just about any time of the year. Plus we plan to go to Kentucky this year in early to mid May. The weather was excellent last year, and I hope it’ll be good this year.