When comparing Jawbone UP3 vs Garmin Vivofit 3, the Slant community recommends Jawbone UP3 for most people. In the question“What are the best fitness trackers?” Jawbone UP3 is ranked 20th while Garmin Vivofit 3 is ranked 25th. The most important reason people chose Jawbone UP3 is:
Foods eaten can be added manually from a comprehensive list and detailed statistics about them can be seen. Foods can also be added by pointing smartphone's camera to a bar-code.
Specs
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Pros

Pro Integrates with Jawbone's free app for logging food & drink
Foods eaten can be added manually from a comprehensive list and detailed statistics about them can be seen. Foods can also be added by pointing smartphone's camera to a bar-code.
Pro Suggests personalized goals to help keep you motivated
A feature called "Today I Will" suggests personalized goals throughout the day.

Pro Highly accurate heart-rate monitor
UP3 fitness tracker uses micro-currents to sense the user's heart rate with extreme accuracy. Currently, heart-rate is only tracked twice a day, but it will be tracked continuously after UP3 has a firmware update.

Pro Advanced sleep tracking
UP3 is capable of detecting light, deep & REM sleep. Correlation between activity and sleep are also recorded so Smart Coach can make personalized sleep recommendations in the future.
Pro App helps you keep track of your goals and progress
The fitness tracker's app is beautiful and intuitive. It allows accessing personal profile, goals, lifeline, trends, team members, app support, inbox and settings. Additionally, status of Sleep Mode can be changed, stopwatch can be started/stopped and power naps, alarms, and alerts can be set up.

Pro Accurate step counter gives you reliable data
UP3 has a very low margin of error when counting steps. For example, it won't count arm movements towards total step count as many other fitness trackers tend to do. As such it will be able to provide more accurate data on calories burned, time active and distance traveled.

Pro 7-day battery life
Running 24 hours a day, UP3 will last a week off of one charge.

Pro Smart alarm helps you wake feeling rested
The UP3 tracks sleep cycles, and its alarm can be configured to take this into account, attempting to select an optimal wake time.
Pro Can be set up to e-mail a weekly summary
Jawbone allows for users to set up a weekly email that will send a summary of their activities making fro an easy way to see what one has done in the last week.
Pro Share with and keep track of friends
You can add friends or just random people and see their activity in your app's activity feed. You can also cheer them on and comment on progress.
Pro Has OLED indicators for notifications & status
Blue light indicates sleep mode, the orange light indicates activity, and white indicates that there is a notification.

Pro One size fits all
UP3 comes with an adjustable strap so everyone can wear the same bracelet.
Pro Logs workout
To automatically track a timed activity, you can set the wristband in Stopwatch mode by pressing + long-pressing the button. You can also enter the activity manually from the app by supplying information on the activity type, effort level, start time and duration.
Pro Allows setting goals, alerts and reminders in order to motivate
There are multiple ways the app tries to motivate. First it asks to set goals and if you are struggling in achieving them, you can set the tracker to remind or alert you via notifications of your connected device or vibrating the wristband itself.
Pro Power nap mode
2 presses + long-press on the wristband will enter power nap mode. Power nap setting, such as how long should you be asleep and your maximum time spent sleeping and awake, can be adjusted from within the application.
Pro Integrates with an impressive list of apps
Jawbone app allows data from third-party apps to be imported as well as Jawbone's data to be used to supplement other apps. When activity is logged in a third-party app it will show up in Jawbone app's feed to give a complete overview of fitness and health situation.

Pro Real-time Bluetooth 4.0 syncing
Bluetooth syncing removes the hassle of having to take the device off of the wrist and putting it back on again multiple times throughout the day. It also allows the device to send notifications to the phone. Bluetooth 4.0 is a great benefit to UP3 users because it doesn't use as much energy as previous versions, which will boost battery life.

Pro Advanced metrics tracking system
UP3 uses Bioimpedance sensors that track respiration, perspiration, hydration, skin temperature, heat flux, BMI, and can even sense which activity is being done. For instance, UP3 can identify sports like tennis and log the information automatically.

Pro Integrates with IFTTT (an automation app)
IFTTT (IF This Then That) is an automation app. By integrating it with UP3 you can get functionality like turning lights on in your room when you wake up, creating a chart of all your data and uploading to Google Drive, log a meal when you check in at a restaurant on Foursquare, etc. You can see a list of over a 1000 public recipes here.
Pro One year warranty
Jawbone will replace any broken device for up to one year.
Pro Completely safe for swimming and showering
The Vivofit 3 is waterproof up to 50 meters. You can confidently take it swimming, or wear it in the shower without risk of damaging the tracker.
Pro No need to recharge the tracker
The Vivofit 3 runs on battery so there is no need to worry about keeping it charged.
With a battery life of up to 1 year, it can go longer without a battery change than most other fitness trackers.
Cons
Con Very limited heart rate utility - Can't take HR during exercise
The UP3 fitness tracker can only measure heart-rate when at rest (including while sleeping). This is because it uses a different technology than other smart bands - so unfortunately active heart rate can't be added in future software updates.
Con There is no customer-service to help you if the UP3 has problems
The Jawbone UP3 fitness tracker frequently has quality issues and with Jawbone not having customer service, your only option is to return it to the place your purchased it from.
In September 2016, Jawbone was forced to end their deal with the customer-service agency due to non-payment. You can read more here.
Con The watch can easily get lost because of the weak clasp
The clasp is extremely unreliable and frequently pops open, especially during exercise.
Con Inaccurate sleep tracking
It shows made up sleeping and heart rate data. Just leave the band off for a night and you'll see heart rate and sleep measurements in the app when you sync the next day.
Con Poorly made and known to malfunction after a short period of use
Along with the major clasp issue, the UP3 has an all-around durability issue. The band has been known to break, the clasp fall off, and the tracker to stop transmitting data.

Con No display
Instead, UP3 has LED indicators that will relay info to the user, but no display, so detailed info will have to be synced with ones app in order to see it.
Con Too unreliable for the cost
The Vivofit 3 has multiple serious issues impacting its reliability which means you're taking a gamble by purchasing it. At $80, you can get trackers with much better build qualities and a similar set of features.
Con Software that detects different activity often doesn't work
The "Move IQ" software in the tracker, which is supposed to detect different types of exercise, often doesn't work. Either it will track everything as walking, or will not start tracking them all.
Con It's easy to lose the watch because of the weak clasp
The clasp frequently comes undone during physical activity because of its poor design. If you aren't constantly paying attention to it or add re-enforcement to the clip, it would be easy to lose the tracker.
Con Syncs with a limited number of devices
Con Not for people with small wrists
The tracker is available in two sizes, regular or extra large. The regular band is too long for people with below average sized wrists.