Commando.
KILL KILL KILL
Commando
Ravager
Saboteur
Synergist
Sentinel
Medic
Commando.
KILL KILL KILL
WICKED-AWESOME SIG.
For playing: Commando by far.
For AI intelligence: Saboteur.
For ease of mind: Sentinel and Medic.
At first I liked commandos (first two chapters), but when I had to make do with Sazh, Vanille, and Hope (none of which have the commando class at that point, mind you), I used ravage-type moves like crazy, and I managed to constantly stagger my enemies, despite the difficult of doing so (for me) without a commando. So, I like Ravagers for the difficulty of increasing the stagger gauge.
Returners Represent!
I like Sentinels, but Saboteurs are awesome.
I usually start with either C/R/M or C/R/Sn., swapping to M/Sy./Sb. when I need to buff and M/Sy./Sn. when I need to stay alive.
Commando, as I like finishing battles quickly.
Str8 Pimpin'