I love them both, but I'd probably go with Christmas Trees because I love the lights and the nostalgia factor; the first time I played an AC game was near Christmas!
I like both, but I'm going to have to give the edge to the cherry blossoms here. I first played Animal Crossing in April 2009 when the blossoms for spring 2009 were in bloom in many areas (unfortunately, you don't have many in the South) and also because I like Japan's culture in general.