i haven’t ever had a ton of friends; the most i’ve ever had was in high school, when i maxed out at maybe 5 good friends. even then, i never really had a “best” friend. 
enter college, and my friend list was whittled down to three or four really good friends, depending on when you counted, and a handful of decent friends. again, i never really had a best friend.
as it stands now, i consider my friends list really small – i have two people i consider good friends. of course i have my siblings and work friends, but even though they are friends, they aren’t 100% friends – they are those other designations as well. 
again, no one is “best”. after some thought, i realize that i don’t really subscribe to the term “best friend”. what does it mean, anyway? this person is the best at being a friend? this person is the person i like best? 
when a gal only has two 100% real friends, it’s hard to put one above the other, especially when they both bring different things to the friend table. if i had friends who were very similar, then it might be easier to label one as the best, but when your friends are different and are a part of and affect your life in different ways, it would be difficult to say one is better than the other. i like them both for different reasons. they are the best at different parts of being my friend.