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Marathon runners and outdoor enthusiasts get the most out of rugged smartwatches like the Apple Watch Ultra 3 or the Garmin Fenix 8 Pro. These smartwatches are a step above your run-of-the-mill activity tracker or classic smartwatch, and they perform better in tougher environments. 

While classic, general smartwatches may perform well in most circumstances, like race training in the park with a few days of battery life, rugged smartwatches typically track more workouts, offer weeks-long battery life, and include brighter, highly visible displays. They are also pricier than mainstream watches, making a deals event like Prime Day a convenient time to save on a high-end smartwatch. 

Also: Prime Day last chance: Save on these deals before they're gone 

The Apple Watch Ultra 3 and Garmin Fenix 8 Pro are similar watches in theory -- and they're both discounted during Amazon Prime Day, which runs until June 26. They're rugged devices with ultra-bright, readable, and vivid screens. 

The devices operate in off-grid areas to reach emergency services or send messages when other devices' connectivity might fail. Their audience is the outdoorsy, hyper-athletic, and active type. 

Still, the two smartwatches boast important differences. If you're considering both, here's which would work best for you. 

Specifications

You should buy the Garmin Fenix 8 Pro if... 

You want the brightest, most vivid smartwatch display 

The Fenix 8 Pro has a MicroLED display with a peak brightness of 4,500 nits. Garmin says the MicroLED technology makes the watch its brightest smartwatch ever. It's a display you can read in peak sunlight without an issue. That display will cost around $2,000, but Garmin also offers an AMOLED display for the Fenix 8 Pro for $1,200. 

You want to charge your watch as little as possible

The Garmin Fenix 8 Pro has a ten-day battery life. That's a week longer than the Apple Watch Ultra 3, whose battery lasts 42 hours, or 72 hours in low power mode. 

Also: The Garmin Fenix 8 Pro smartwatch is a top-selling Prime Day deal - here's why I recommend it

You're ready to splurge for the industry standard

The Garmin Fenix 8 Pro is one of the more high-end rugged watches you can buy. You're getting this watch for its sheer breadth of activities it can track and ultra-rugged design. You'll get more data from your workouts and recovery when you train with the Garmin than you would with the Ultra 3, including a hill score, recovery and sleep scores, daily suggested workouts, and a sensor for attaching to a golf club or bike. 

It also comes with a handy flashlight that ZDNET's Matt Miller has raved about. As a bonus, the Garmin Fenix 8 Pro works with both Android and iOS devices, whereas the Apple Watch Ultra 3 is only compatible with iOS.  

You should buy the Apple Watch Ultra 3 if... 

You want a rugged smartwatch with the capabilities of a smartphone 

The Apple Watch Ultra 3 is certainly rugged, with a higher waterproof and dust-proof rating than the other smartwatches in the Apple Watch lineup, standalone satellite communications, and topographical maps for national and regional parks. 

But it is also a smartwatch that people with larger wrists (or those who want larger screens) wear every day to go to the office, exercise, and more. You could get lots of use out of the Apple Watch Ultra 3 without ever using it during an Iron Man or Tough Mudder. The Garmin Fenix 8 Pro, on the other hand, is built specifically for those rugged, outdoorsy moments. 

Also: Our favorite health trackers are disappearing - and that's the point

The Ultra 3 is a great watch for people who work in conditions where they can't always check their phone, but still want to stay connected and receive communications from their wrist throughout the day. And because Apple excels in making beautiful software, the UI on the smartwatch is a little bit more comfortable and intuitive to navigate than Garmin's.  

You're in the Apple ecosystem 

The Apple Watch Ultra 3 is only compatible with iPhones, while the Fenix 8 Pro is compatible with iPhones and Android devices. You won't be able to download playlists or music from Apple Music on a Garmin smartwatch.