Here are the agent classes from weakest to strongest

D-Class: Only 50 known

C-Class: Only 30 known

B-Class: Only 20 known

A-Class: Only 15 known

S-Class: Usually Leaders; only 5 known

SD-Class: Usually Commanders; only 12 known

SDA-Class: Usually run each region; only 14 known

Master SA-Class: Strongest of all; only one known