Guess what: Fitbit's newest tracker is its best one yet. There are a lot of Fitbits to choose from, but after wearing all of them, the Fitbit Alta HR wins our vote. It has almost all of the same features as the Charge 2, our old favorite tracker, but in a design that is 25 percent slimmer with better battery life. The Alta HR has continuous heart-rate, basic phone notifications, and after wearing it for weeks it's proven to be a great fitness companion.

For me, it's all about design. I've been wearing the Alta HR for almost a month and plan to continue wearing it even after this review. It's comfortable to wear and doesn't sacrifice any features, but what sold me was the seven day battery life. Now if only it were swim-proof like the Flex 2, then it would have been a grand slam.

The Alta HR costs $150, £130 or AU$250, the same price as the Charge 2. For most people, the Charge 2's extra few features probably aren't worth it. If you do care about manually tracking workouts or having a stopwatch, get the Charge 2, otherwise the Alta HR is the fitness tracker we recommend.

A slim heart rate tracker

Fitbit's heart rate tracking has finally found its way into a smaller band. The Alta HR is the same size as the original Alta, and has all of the same features, plus heart rate. It can track steps, distance, calories burned, active minutes and sleep. To look at these stats, just tap the Alta HR's case below the screen (the display isn't touch-sensitive, but the Alta HR can detect forceful taps). Unfortunately, it doesn't do stair climbing or have a "Relax" mode like the Charge 2.

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The tracker's narrow monochrome LED will also display notifications for incoming calls, text messages and calendar alerts, and will provide reminders to move throughout the day. As I said with the original Alta, though, these notifications can be difficult to read due to the small display.

The heart rate sensor measures heart rate at 5-second intervals continuously throughout the day. This is the same as the Charge 2 and Blaze, but both of those can also manually start workouts which increase the sample rate to once every second. In everyday use over a few weeks, I didn't miss that faster heart rate sampling, but serious workout warriors might.

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The Fitbit app provides a graph of all-day heart rate and resting heart rate. It also displays a personalized Cardio Fitness score. This is the same score that debuted last fall on the Charge 2 and is slated to arrive on the Blaze. It's an estimate of overall health that is based on your VO2 Max, a widely accepted metric that is used to determine how well our bodies can use oxygen during workouts.

A stylish tracker with long battery life

The Alta HR supports a wide variety of swappable bands. There are rubber ones in multiple colors and even more stylish leather and metal options. The straps from the original Alta will work with the Alta HR (and vice versa). Swappable bands also mean less wear and tear on the actual Fitbit device.

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While the straps are backward compatible, the clip-on proprietary charging cable isn't. Luckily, you won't have to charge it often. The Alta HR will last an entire week on a single charge, which is damn impressive given the small size.