I'll start with two sets of friends:
Alicia and Kattar (Damsel in the Red Dress) aren't very alike in most ways. At first glance they seem similar. They are both Mexican-American, raised by single mom's who rarely saw their fathers. Both worked in artistic media/art centered careers, and they even LOOK rather similar. But their personalities are very different. Kattar is a socialite and Alicia is introverted on the best days, suffering from social anxiety on others. She has a little brother she loves to bits and he's an only child. She gave up everything for the sake of her little brother while he's always had basically everything a child could ever want. And the way their mother's raised them was fundamentally different in almost every day.
However, the ways they connect would make them seem more similar than they are different, so it's hard to tell where they fall. They both are caring in nature, willing to self-sacrifice their time to do things the other is interested in without complaining. They both love through acts of servitude.
So it's really hard to tell if they're more similar or more different.
Then there are Hallie and Mad (Hushabye Prince), who at first glance are extremely different. One tall one short, one feminine, one tomboyish. One loud and bratty, one elegant and suave. But then on closer inspection they are basically the same person divided into two bodies lol.
Lot's of people talk about their friends balancing each other's weaknesses, but I really think I lean more toward two peas in a pod, how about you?