What's the best way to do cardio: Treadmill or Elliptical?

I've been asked this question almost every day, so it's clear that most of you have grappled with this question at one time or another.
First and foremost, you should stick to the machine that you enjoy using--whether that's biking, treadmill, elliptical, or even rowing machine--and do it consistently. The most important thing to ensure that your cardio workout is effective is keeping your heart rate between 60 to 85 per cent of your maximum heart rate. The easiest way to determine your maximum heart rate is by subtracting your age from 220. For example, if you are 30 years old, your maximum heart rate would be 190, which means your optimum heart rate for cardio exercises would be between 114 and 161 bpm depending on your fitness level.
Last but not least, you should alternate your activities and change up your routine every 2-3 weeks to avoid reaching a plateau.