And for everyone, do you have a favorite cardio machine you use? Why?
Any of them will work fine if used diligently, but that's the thing. You may get better results by working physical activity into your daily routine (especially long term) than by carving out a slice of time to go to a gym. Take the stairs rather than the elevator. Instead of watching TV or playing on the internet in the evening, go for a walk ro bike ride around the neighborhood. Ride a bike to work if you can, or get off the train/bus a few stops earlier and walk briskly. When it starts seeming easy, increase the distance, increase the pace. If your situation is such that that's not doable and you don't have any choice but to drive from your door to your workplace and work at a sedentary job all day, a gym is a good answer, but if you can work physical activity into your daily routine, you may have better luck at being active consistently than if you try to make time to go to a gym.