主句是主系表结构.主语：The best kind of friend 系动词：is 表语：the one
you到句末是定语从句.
定语从句的主语是you 定语从句中有三个并列谓语：could sit,say,walk
句中没有形式宾语那feeling like it was the best conversation you've ever had这句算什么成份feeling like it was the best conversation you've ever had是现在分词短语做方式状语，修饰walk away,其中it was the best conversation you've ever had是省略that的宾语从句。仅供参考