X-box with Kinect. There are some great games on Kinect that your girls will love and are easy to play.
The Wii technology has stood still for the past two years and has not moved forward with time. For their games, you still have to hold a controller in your hand. If you then shake the controller, the wii thinks that you are moving.
With Kinect, the sensor mirrors the body image in front of it so, no need to hold a controller. However, this does mean you cannot cheat with the fitness programmes
but for the girls dancing etc it is just great.
Our Wii has not been played with for over a year, since we bought the X-box. With X-box live, the girls would also be able to chat and play with their friends which makes gaming very sociable.