one
If you don't already own an Apple Watch, you can buy the SE(New generation), S7 or S8 depending on your budget.
two
If you have an S7, there's no need to upgrade. (Note :S8 compared with S7, in the hardware configuration, Apple upgraded its temperature sensor, accelerometer and gyroscope, and has IP6X dust rating; In terms of software functions,S8 adds car accident detection and female menstrual management functions)
three
If you are currently using the S6 below (including S6)- SE(first generation) above (note :S7 compared to S6, the screen has become larger, and the new fast charge and color matching), then you can upgrade to S8 according to demand (because S7 and S8 prices are similar).