It depends on the game for me. In ANB I like spring best, because I get bored of the winter colours quickly.
In games where there are less crops in winter though like FoMT, or even none, winter is my favourite. Purely because it's nice to have a break from crops and focus on my animals, and do other tasks that take up time. This would have actually been really useful in ANB. I suppose in theory I could just pretend there are no crops to deal with... but there are star levels to raise!
