There is no denying the popularity of fitness trackers. With over 20 different brands on the market, which one should you choose to get you moving?

For two weeks, we alternated between wearing the FitBit Flex ($100) and the Jawbone UP24 ($150) fitness bands to determine which is better suited for our active lifestyles. Both bracelets have the same goal, but they also have a few notable differences.

Comfort, Style and Fit:

The Flex and UP24 are equally comfortable, both being made from rubber. The Flex's adjustable band allows for a more snug fit, but the clasp makes it a challenge to put on one-handed. We found that the UP24 is easier to put on and take off because it doesn't lock around your wrist. The UP24's slim, minimalistic design is also a plus for those concerned with style; we didn't feel the need to take it off at happy hour.  

However, the UP24's design advantage was short lived when it was knocked off our wrist during a full-court pickup game. In this case, the Flex's sturdy clasp would've been a welcomed feature. 

Fitness Tracking: Both bands use body movements to calculate the number of steps you take during the day and allow you to log different types of workouts at varying skill levels.

Screenshots of the Fitbit Flex app (left) and Jawbone UP24 app (right).

Yet, it should be noted researchers have found that while most trackers are fairly accurate (10-15 percent error) in monitoring calories burned, not all devices are created equal. A June 2014 study by researchers at Iowa State University compared eight popular fitness trackers to a medical-grade metabolic analyzer. The study found that Fitbit products recorded a 10 percent error rating and Jawbone products at 12 percent.

To see the differences, we tried and tracked our calorie burns during four very different workouts in the UP24 and Flex apps:

Racking up steps during runs can be rewarding, but we found that the bands weren't able to similarly track our movements during other workout sessions.

According to both bands, in a 75-minute high-intensity boot camp class, we burned less calories than on our easy, 25-minute training run days. Plus, after a low-impact 55-minute class at Pure Barre, as far as both trackers were concerned, we might as well have been stuck in our desk chair. True enough, our wrist wasn't moving much at the bar, but our shaking leg muscles told a completely different story.

The same went for our warm-up on the stationary bike before weight training sessions — neither of the bands seemed to register the movement, skewing the count of calories burned.

Motivation: The Flex's display has five tiny LED lights on the band that, when you double tap on the display, indicate how close you are to reaching your targeted steps. In testing, the feature proved to be motivating – when it worked. In some cases the "gentle tap" needed to activate the LEDs turned out to feel more like a smack.

The UP24 doesn't have a display, but it does have a unique alternative. The bracelet can be set to get you up and moving by way of a gentle vibration. For those with desk jobs, we found this feature useful.

Sleep Tracking: Both bands offer a bar graph of your sleep patterns — how many times you woke up and how long it took to fall back asleep. The downside is that in order to track sleep patterns, you need to manually alert the bands that you are in sleep mode.

It's worth noting that many sleep experts question the accuracy of fitness bands' sleep tracking, especially in regards to different sleep cycles. The bands work to detect the wearer's sleep through tiny motion sensors called accelerometers.  In layman's terms – if you're awake, you're moving. If you're asleep, you aren't moving much. Yet sleep researchers have said that you move the same amount whether you're in deep sleep, or lighter stages of sleep — so take it all with a grain of salt.

Do you need a $100 fitness tracker?

Go for the Jawbone UP24 or Fitbit Flex if you're a fitness newbie who is looking for a little extra push to stick to your goals. The bands proved to be motivational even if the logging capabilities weren't entirely accurate.

For those with set exercise regimens, it's probably better to invest in a heart rate monitor.