The main quality all my friends have in common is that they are all actual friends.
I don't have many friends, just a few.
I'm not talking about the people I know, say hi to, or see often, those I have a lot of, but those aren't the ones I would necessarily consider to be my good friends.
My good friends are the ones that, even if months go by without us talking, we will continue being friends as if no time has passed at all.
The ones that, whether they know me best or not, respect me and are there for me, even if we don't agree on things.
The ones that I can share things with and that they share things with me.
I don't need or really care if I have many friends or not, I can get by perfectly with just a few of them, a few really good friends.
One good friend is better than 10 not-so-great friends.