You mean the class or Job 'Derplander' has in each opening movie? It varies, but it's more or less like this:

1.0: GLA in the Adventurer's Guild but changes to ARC within an Echo scene
ARR: WAR
HW: WAR then changes to DRG during the defense of Ishgard
SB: MNK while training against Lyse in Rhalgr's Reach, and SAM in Kugane
SHB: SAM during the Battle of Gymhlyt Dark, then cycles through ARC, WAR, DRG, MNK, SAM and finally DRK while fighting the Sineater in the First.