The LG Watch Sport is a big smartwatch, but it doesn't quite reach the considerable proportions of the Gear S3.
Both watches have stainless-steel bodies, though the Watch Sport uses plastic on the wrist-facing side.
The LG Watch Sport ships in both titanium and blue color options, while the two editions of the Gear S3 (Classic and Frontier; the Classic model is pictured in this comparison) each only come in one hue.
Both watches work with recent Android phones.
In a change from recent years, both Samsung's and Google's watch platforms can now play nice with iPhones.
While both watches are large, LG managed to squeeze in a better screen-to-front-face ratio, with its 13-percent bigger display.
The Watch Sport has an unusually high-resolution display for a smartwatch, with a 25-percent higher pixel density than the (already-sharp) Gear S3.
The Sport uses P-OLED (Plastic OLED) display tech, while the Gear S3 has an AMOLED panel.
We're looking at two different variants of Gorilla Glass: Samsung opting for the newer (wearable-focused) SR+, with LG sticking with older Gorilla Glass 3.
If you thought Apple's tech-industry influence had dropped in recent years, this category might make you think twice. The LG Watch Sport pinches the Digital Crown from the Apple Watch. (Here it's called a rotating power button.) While Samsung's scrolling bezel on the Gear S3 isn't as direct a knockoff of Apple's idea, it's a similar idea with a different placement.
Despite the apparent lack of originality, we prefer these kinds of scrolling methods over repeatedly swiping on a touchscreen (though you can do that too, if you prefer).
You can buy both watches in standalone, LTE-connected models, though cellular is standard on the LG Watch Sport but only an optional variant of the Gear S3.
Both watches also have GPS, so you can track your location without the help of a paired smartphone.
Both have strong IP68 water resistance, meaning they can hang out in up to 1.5 m (about 5 ft) of water for up to 30 minutes. Swimming, however, isn't a good idea with either.
The LG Watch Sport has a bigger battery, though it also has more pixels to drive in its display. We'll test the battery life of a review unit soon.
Each smartwatch can keep tabs on your pulse.
You can swap out the Gear S3's band for standard 22-mm replacements. The Watch Sport can't pull off this trick, since it has antennae inside its band.
This should be a pretty dramatic difference: The LG Watch Sport includes Google Assistant, the same AI found in the Pixel smartphones. Samsung's S Voice, by comparison, is a watered-down Siri knockoff.
Both watches let you pay with your wrist, though Samsung Pay has the advantage of working with most standard credit card readers (no NFC equipment required at the store).
Onboard app store
On the Gear S3, you have to install smartwatch apps from your phone, which then automatically pair with the watch. With Android Wear 2.0, watches like the Sport get their own watch version of the Google Play Store that can install apps sans phone.
If you don't fancy talking to your wrist like a modern-day Dick Tracy, both watches have keyboards and handwriting options.
We're looking at Android Wear 2.0 vs. Samsung's Tizen OS.
The LG Watch Sport is now shipping, while the Gear S3 has been on store shelves since last November.
Starting price (full retail)
These two high-end wearables are going to cost you, at an even $350 (though Verizon charges $380 full-retail for the Sport). You may, however, be able to buy on an installment plan that spreads the cost out over a couple of years.