We're voting for # 1 because it has both of them, they are looking right at the camera and its at an unusual angle so it caught our eye. Maybe crop it so just their cute little faces are in the photo. (Didn't Kay say face shots were a good thing for the calendar?)
Anyway, that's our vote. But if you do decide to go with a single kitty photo - we like #6 too.

I'd like to see all the photos that everyone ultimately decided to send in.