The definitive Fitbit buying guide reviewer and fitness fanatic James A. Martin used and tested every product Fitbit has ever released, including the new Charge. This in-depth buyer's guide will help determine which of the current six Fitbit models is right for you.

Do you have your eye on the new Fitbit Charge? Or would you rather a Surge, Flex or Zip?

You can now choose from a total of six different Fitbit activity tracking devices. As a longtime Fitbit user, I've tested all the available models, along with two trackers that were discontinued (Ultra and Force), as well as the company's Aria Wi-Fi-connected scale. If you're thinking about joining the sweaty ranks of Fitbit users, here's a guide to help choose the right device for you.

Fitbit Zip

Pros: At $60, Zip is Fitbit's least expensive device [ Find it on Amazon *What’s this?* ]. Unlike other Fitbits, Zip uses a replaceable 3V coin battery that the company says last for six months. It also comes in five colors, but if you seek the most color options, you might want to get a Flex.

Cons: Zip is also different than other Fitbits because of its LCD screen, which isn't backlit and therefore is impossible to read in the dark. Zip is the only Fitbit that doesn't track sleep or provide silent alarms. Like Flex, it doesn't track stairs climbed, either. And like One, Zip — because it’s not worn on the wrist — can be easy to lose or inadvertently ruin in the washing machine, if left in a pants pocket.

Ideal Users: People who aren't particularly tech savvy, are just getting started in fitness tracking or who don't want to mess with recharging.

Fitbit Flex

Pros: If you buy a Flex ($100), you can choose from 10 wristband choices, many of which are sold as optional $30 three packs, as well as Tory Burch fashion bracelets ($38 to $195). Flex differs from other Fitbits in that it's a little "pod-like" device that you snap in and out of a wristband, which makes it simple to change wristbands from one color or style to another. It's also water resistant, so you can wear it in the shower — a rarity for Fitbit [ Find it on Amazon ].

Cons: Flex doesn't count stairs, and there's no display, other than LED lights (no actual step count) that illuminate to indicate how close you are toward meeting your desired goal.

Ideal Users: Fashion-minded folks who want basic activity tracking.

Fitbit One

Pros: One ($100) is my preferred pocket- or belt-worn Fitbit. It's more compact than Zip and, unlike that low-end model, it tracks sleep and stairs climbed. One is available in black and burgundy [ Find it on Amazon ].

Cons: The One's OLED screen is difficult to read in bright sunlight. For sleep tracking, you must wear One in the provided, but awkward, arm- or wristband. Like Zip, One — because it's often carried in a pocket — can be easily lost or ruined in a washing machine.

Ideal Users: People who don't want to wear an activity tracker on their wrist and want to track sleep and stairs-climbed.

Fitbit Charge

Pros: For $130, Fitbit's Charge wristband [ Find it on Amazon ] offers more features than Flex. It shows you caller ID notifications on the OLED screen, provided you sync your compatible smartphone via Bluetooth. (Caller ID is also available on Charge HR and Surge.) Like Charge HR and Surge, sleep tracking is automatic; you don't have to activate or deactivate sleep-tracking mode. Battery life is good, especially compared to the short-lived Charge HR and Surge. (For more details, check out my full Charge review.) It's available in four colors.

Cons: Setting up Caller ID was more challenging than I expected, the small screen can be hard to read, and it's not water resistant.

Ideal Users: Charge has a mid-range feature set — more than Zip, One and Flex, but less than Charge HR and Surge. It's is best for people who usually buy tech products that fall somewhere between low- and high-end.

Fitbit Charge HR

Pros: For only $20 more than Charge, Charge HR [ Find it on Amazon ] offers all the same features plus continuous heart-rate monitoring (no chest strap required), which is particularly important for athletes who want to get the most out of their exercise. It's available in four colors.

Cons: Fitbit says Charge HR can last for up to five days on a battery charge. In my experience, actual battery life is much less. For example, less than 24 hours after charging, and following a one-hour run using continuous heart-rate monitoring, Charge HR's battery dropped to 50 percent. You can turn heart-rate monitoring off via the Fitbit app, but you need to remember to turn it back on before exercising.

Ideal Users: Athletes who want to track their heart rates during exercise but don't want the bigger, chunkier Surge or another GPS watch.

Fitbit Surge

Pros: Surge [ Find it on Amazon ] is the ultimate Fitbit device, and despite its chunky size, it's my favorite Fitbit wristband. Unlike other Fitbits, Surge uses GPS to track your routes and display them on a map. You can control features and functions on the device itself, such as choosing different types of exercises to record, instead of having to use the app. It displays SMS alerts and caller ID information. Surge's screen is always on, so you can quickly check the time, and it displays multiple activity tracking data on a single screen during exercise, including distance traveled, elapsed time and current heart rate. The device also lets you control music playback on your connected smartphone. Surge is a super activity tracker with a few smartwatch features thrown in, and it's available in three colors. (Read my Surge review for more specifics.)

Cons: Surge is unfortunately chunky; I have trouble sliding buttoned shirt cuffs over the device. Like all other Fitbits except for Flex, it is not water resistant, so swimmers should look elsewhere. Like Charge HR, the battery only lasts about a day if you use continuous heart-rate monitoring and track an exercise. If you want to track your sleep, you'll need to find a way to recharge the battery during the day. (I recharge it while working at my desk.) At $250, it's also rather pricey.

Fitbit Apps

Fitbit's mobile apps (for Android, iOS and Windows Phone) are worth mentioning for several reasons. For starters, you don't even need a Fitbit device to track your steps — the app tracks steps on its own. Fitbit's apps recently added an exercise-tracking mode, which uses the GPS on your smartphone to track your route, which could dissuade some people from buying Surge.

Also, in January, Fitbit announced a new software feature that will let you have up to five Fitbit trackers connected to one account is "coming soon." In theory at least, that should make it easy to, say, wear Surge when you're exercising and Charge HR the rest of the day and night.

Why Fitbit?

I've tried a number of activity trackers, including Garmin's popular vivosmart. Despite some limitations — no support for cyclists and swimmers, they don't work with Apple's Health app — Fitbits are still my favorite, by far. You have plenty of device choice. The app is easy to use, though initial setup may be problematic. The software offers a lot of features, but not so many that they are overwhelming. Connecting with other Fitbit users is a great motivator, and Fitbit plays well with third-party apps such as My Fitness Pal and RunKeeper.

The only real question for me: Will I still want to wear a Fitbit when Apple's Watch finally debuts in April?

Copyright © 2015 IDG Communications, Inc.

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