BEST
#1 WHM : required for nearly everything exp parties even when RDMs were "kings", and now much greater than RDM. DNC, SCH or ... PUP never could compete and always were compared to WHM in a negative way ("it's cool but it can't do this that WHM can" kinds of comparison).
#2 MNK : uncontested DD for nearly every situation. The only DD that is equivalent is WAR and the only thing WAR can do beside monk is provoke which would never be used even at low levels. Can tank and DD. Most DDs have always been gimp compared to those except maybe relic DRK back at 75. SAM has always been overrated mostly due to auto capping weapon skills stats. Used to be optimal in low man engame (from limbus, dynamis, salvage to abyssea, and adoulin).
#3 BRD : the only buffer of the game. The others are good only when there is a bard which makes them pointless nearly all of the time. It's the first in its category though overall it's not really needed for low man endgame, just makes it ton faster.
WORST
JOB Failures : PLD (can't tank with DDs), Rune Fencer (wtf job).
