Walking stresses the joints least, but jogging and running will burn more calories per minute. The treadmill surface can be hard. If you plan to run or jog, investing in a surface with more give is worth it. A 1 to 1 horsepower motor is best If you plan to walk only, you can get by with a narrower treadmill belt, but it should still be at least 5 feet long. Make sure the handrails can support your weight should you lose your balance.
Some treadmills come with resistance levers for upper body exercise.
But they may feel awkward during a long workout. Holding the handrails reduces the workout intensity. Once you have mastered the technique, keep your hands off the rails whenever possible. When walking or running on a slant, maintaining good posture with only a slight bend at the waist is best for your back. Exercise bikes provide fairly intense workouts with little stress to the knees.