Madara and Hashi were not best friends their friends were their brothers. Kakashi and Guy have the best friendship check the episode when Kakashi was about to be Hokage
The best couple are those who are each others best friends as well. You're right, Kushina and Minato has shown it more than anyone else. They weren't just spouses, I say they were best friends too. You know, you can't like anyone more than you lover!
Some times men enjoy to spend their free time with theri friends more than their family. Shikaku Nara reminds me of that kin of men!!!