21” - looks better, less range, feels the road more (pro or con depending on your view), sticks to the ground more on turns and high accelerations, more likely to be dented by a deep pothole, more likely to get curb rash. Summer tires mean worse for snow.
19” - thicker sidewall means more range, feels road slightly less (a bit more floaty), spins (but stays planted due to traction control) in launch mode or high acceleration, looks worse, less likely to be dented or get curb rash. All season tires, so better for snow.
20” - no idea, I don’t have them