What principally distinguishes the transmitter tiers in “three tiers of people” here?

The Compilation Method: Narrator Tiers, Justified Repetition and Abridgement

• Only the chronological generations of Companions, Successors, and their Successors
• The subject matter of reports: worship, transactions, and manners
• Transmitters’ relative standing, especially memory, precision, accuracy, and reliability
• Modes of receiving hadith, such as audition, reading to a teacher, and authorization