There has been lots of Spiritual masters (I'm avoiding the word Guru deliberately, because of such rampant misuse of it) who were proponents of various sects of Vaishnavam such as Madhava (Brahma-Vaishnavam Sect, ब्रह्म-वैष्णवं), Shridhara Swamy (Rudra-Vaishnavam Sect, रूद्र-वैष्णवं) etc.
What were the main identifying factors of these sects or sampradayas (सम्प्रदाय)? What differentiated these from each other and from themselves?