I second Sparrowsabre's comment, Family members are great and all but you can talk to your friends about more things than you could with a family member - would you really talk to a sibling or parent about sexlife or other intimate things like that?
For the most part my best friends know me more than anyone else, second to that is the gf (because we've grown up together my friends have been there for nearly 10 years now, the gf's only been about for 2.5years) Friends you went to school with you tend to grow up with and see more in the day than you would a family member anyway.
Family is important to me though, why else have the word family tattooed onto me if i didn't believe in what it is/means
Growing up gives birth to independence and free thinking, you become your own person and in light of that you naturally grow away from the family unit as you get older, for some its a hard to deal with thing and they try t hold on, for others its not even a problem but regardless; family will always be there for you in one way or another (even past family can help if you believe if you believe in some kind of divine intervention that helped you in the past or merely advice they gave you before their end)
As for which is more important, to me they are equal; my family see my best friends as family and to lose any one of them i would feel equal sadness.
Thing is, they both help you through life so no matter what is said they are equal; who helped you get up and learn to “get back on the horse” when you fell and hurt yourself or had your first relationship go wrong? Family. Who was there to drag you out of the club/pub when you’ve had enough to drink and make sure you got home? Friends. Who was there to change you as a baby? Family. Who was there to have a laugh with during bad times? Friends
One half covers you at home, the others cover you whilst out until your strong enough to deal with a lot yourself and by that stage you’ve got a partner and a job lol so yeah they are both as important as each other.