Difficult question, probably change my mind depending upon when I answer but for now:
1) December, always, Can't beat Christmas and the anticipation, plus possibility of snow
2) June, live in hope for a long hot summer
3) April, true spring after a long, usually frustrating, winter
4) October, autumn colours with the prospects of a real winter on the horizon
5) May, spring with a hint of summer
6) November, anticipation of Christmas and winter snow
7) February, an if only month...but you never know
September, perhaps an Indian summer
9) July, summer again
10) August, hopefully summer again
11) March, end of winter but usually not quite spring
12) January, the big anticlimax month unless it really snows, but usually not.
Very subjective, and would probably change the order in a months time, but for now that' s it...