I have Just Dance 2, Zumba, DDR3 and Just Dance. I find that they are all great calorie burners. I set DDR3 for 100 calorie burn which turns into a lot more on my heart monitor. Then I go to Just Dance 2 and set it for workout mode which is the sweat meter and, I believe it is 4 songs. I like just dance because I like the songs. Zumba makes you go through a bunch of training sessions to get to the main stuff and I have finished that part yet.
As far as knees with any of them, just do as much as you can do. I find they all put in a lot of the moves you would do with a normal workout.
Nina- Wisconsin CST
Together Everyone Achieves More
Co-Leader- Walk it Out
Co-Leader- Wii Exercise