The sum up of the classes above is great. My thoughts is firstly play what you have fun playing; but to really test that? Get them at least to 30. I'd recommend getting all three melee to 30, do their job quests and run a dungeon on them. See how you feel about them.

I can't talk about monk, as I can't seem to level mine past 15. My DRG is 34 (for its cross-class, Blood for Blood) and after about 25ish was a lot more fun then it was 1-24 for me. My Ninja is 50. This is quite the accomplishment for me being as I normally avoid melee classes. While my Bard is my main class, I'll play Ninja as much as possible and it helps that they share accessories.

Mudra Lag...SUCKS. It can sometimes be their whole problem. Worst lag I've had was about 5-6 seconds before they'd register so I stopped using them for that fight unless it was just one. This is a huge dps loss that Monk or Dragoon don't have even when the player is lagging.

Anyway, good luck picking your class/job!