The Series 5 has a 1.57-inch or 1.78-inch screen (for the 40mm and 44mm models, respectively) while the Watch3 has a 1.2-inch or 1.4-inch screen (for the 41mm and 45mm models, respectively). The Series 5 offers more screen real estate Going by Samsung's estimates, the Watch3 beats the Series 5 in terms of battery life.