Hello there Malik,
Running or jogging including the Thread mill makes an impact on the joints of ur legs. To generalize every exercise has got its own positive and negative effects on body. Running on a thread mill has less effect on ur leg joints when compared to the freestyle running outside on the roads. But on the other hand an Elliptical bike or a cross trainer, it minimizes the amount of pressure on ur joints besides burning same or even more calories than a Thread mill in a given time.
Not to forget that Elliptical cycle gives u a complete body work out and I specially think the cardio mode or Hills/ Valleys mode works extraordinarily to burn maximum calories.
Just to add it is my personal favorite to loose weight..!!!
Therez a guy on Youtube called scooby, search for scooby workshop....he stresses on doing cardio for atleast 40 minutes morning and evening everyday if u r serious about loosing weight....!!!