You know at least a few people who are convinced they have a "best side." In group photos they always have to stand a certain way. Or if you take a selfie with them, they always need to be on your left or right.
Maybe they think it's their hair. Or their facial structure. Or something. Whatever it is, they're convinced they have a best side.
And if they think their best side is their left side, they're right.
According to research published in Experimental Brain Research, men and women were asked to rate photos of ten male and ten female faces; images showing the left side of the face were perceived and rated as "more pleasant" than photos of the right side of the face.
In fact, respondents displayed a "strong preference" for left-sided portraits.
That was even true when photos were presented as a mirror image, meaning the actual right side appeared to be the left side.
Respondents' preferences were confirmed by measurements of their pupil size, a reliable unconscious measurement of interest. (Our pupils dilate when we're presented with interesting stimuli, and contract when we look at less pleasant stimuli.)
Why do we prefer other people's left sides? That's a little less clear; researchers speculated that "left cheeks tend to exhibit a greater intensity of emotion, which observers find more esthetically pleasing."
So if you're in doubt about what is your best side, assume it's your left side -- and when you're taking a selfie, or being photographed, turn your face slightly to the right so you show more of your left cheek.
After all, it worked for her.