The month of May tends to be my favourite.
It's (usually) warm, things are growing, there's still at least four to five more months of warmth and sun.
The bright greens everywhere is one of the best parts. I hope, someday, to get out of the city (in terms of permanent residency) and back into an environment that the seasons mean a bit more. Sure, Hamilton is greener now that it is May, but in less proportion than in a less urban setting.
When I am out of the city though, its easy to get messmerized by all the green.
(Photo taken in Hamilton, Ontario.)