My opinions:

Job skill requirements to be adequate (highest to lowest)
MNK > SCH > DRG > WHM > WAR > SMN > BRD > BLM > PLD

Job responsibility in a normal setting (highest to lowest)
PLD/WAR > WHM/SCH > MNK/BRD > SMN/BLM > DRG

Job skill required to be exceptional (highest to lowest)
MNK > PLD > SCH > WAR > WHM > DRG > BRD > DRG > BLM

Generally, the lower skill it takes to be adequate, the higher your responsibilities are in an average setting. Subsequently, the more responsibility you have, the harder it is to become an exceptional player, due to skill balance and resource management. With the exception of BLM which I think is faceroll easy to play and doesn't end up with a lot of responsibility in most cases through at least T4.

Again, my personal opinion - I have played every class but BRD @ 50 across my two characters.