My favorite theme was definitely Everest Month!
It was a lot of fun collecting ice cubes from the Pirates game. I remember I was sick from school one day and pretty much played Pirates all day long. It was cool getting the Everest Costume and also keeping up with Yeti Vision as new stages and prizes were released. I liked how Everest Month was extended 2 weeks into March, prolonging the fun. To me, it was the most organized theme, limiting the frustration that always seemed to be present throughout the game.