Features that count

Display

Look for a clear display with easy-to-use controls. A good display will show some combination of your heart rate, calories burned, speed, and incline levels, and details such as time and distance.

Adjustability

For treadmills, consider the machine's speed and incline. The top speed on the models we tested ranged from 12 miles per hour to 8 mph. Most treadmills have a maximum incline of at least 10 percent, but some max out at only 5.5 percent, and one machine, the Esprit ET 188, had no incline at all. Look for machines with programs that allow you to adjust routines based on your fitness level and have heart-rate-controlled workouts that consider your age, weight, and gender.

Heart-rate monitor

Those with a chest-strap heart-rate monitor are best because they don't impede your movement. Contact monitors measure your heart rate only when you're holding onto them, which can impede your natural stride. But it doesn't need to be a deal-breaker; stand-alone heart-rate monitors are available for about $28 to $100.

Resistance

Look for a machine that is easy to adjust and has a variety of workout levels. Treadmills offer a range of speeds and inclines. Some can simulate running or walking downhill.