Best for: enthusiasts who require the best of the best. As with all things Apple, the Apple Watch takes fitness trackers to the next level, measuring workouts like running, walking, cycling, yoga and dance. The Series 6 offers a built-in blood oxygen sensor, heart rhythm checker with ECG app, an Always-On Retina display that is 2.5 times brighter outdoors when your wrist is down and more. It’s water-resistant so you can push yourself in the elements without worrying about damaging your investment. This is the top-end option for true enthusiasts, and one of the best fitness trackers around.