Classes: Leader, Advisor, Star, Writer, and Technician.
Toby Ziegler is a dual class Advisor/Writer. Sam Seaborn was a Writer, but in season 4 he decided to multi-class to Leader. The control room guys in Sports Night and Studio 60 are Technicians. Nancy McNally (the National Security Advisor) is dual class Technician/Advisor.
Danny Tripp is a director, which I think means he’s a dual class Advisor/Writer, emphasis on the Advisor. Hard to say, though.