Kacbu lists 49 Smartwatches with an OLED display: Amazfit, Apple, Fitbit +7. The family is assembled by hand from what each maker calls its panel; the values it includes are listed below one by one, each with its own page.
The maker's own name is kept as written; every value has its own page.
In an OLED every pixel makes its own light; there is no backlight. Black is therefore truly black, contrast is very high and the panel is thin. The price is a risk of image retention on bright static content over time and, at low brightness, sensitivity to flicker; look at the maker's declared PWM frequency and peak brightness.
Each card carries what sets the product apart. Open the product page for its strengths, weaknesses and alternatives.