Which is better for fitness games, Xbox Kinect or Wii?

I'm considering getting either an Xbox with Kinect or a Wii so that I can use their exercise games. Some days I just can't make it to the gym and I thought that this way I could still get a workout at home. The thing is that I am lost when it comes to which console to get. Which is a better workout? Which has more variety in those sorts of games? I don't really care about the graphics, just want to get the most for my money and get a good workout. Any help would be appreciated, thanks in advance!