I don't hang out with my best friend or even share a lot with him, but I can definitely trust him with my life. I've known him since birth really, and we're really cool with each other. :yes:
I have best friends, not just a best friend -- best friends. Asking me to choose which one is my favorite is equivalent to asking a mother who her favorite child is. She doesn't have one, because she loves all of her children equally.