This, my friend, depends entirely on your style.
Black Mage is a Disciple of Magic, so he fights at range, uses MP and deals gigantic burst damage both to single target and to group. There is only one job that can deal more damage to a single target in the same amount of time, Monk, and it requires a very skilled player.
Dragoon is a Disciple of War, fighting in melee range and requiring a lot of positioning shenanigans. However, it is an excellent DD (if a bit frail), in fact it can give Monk a run for it's money, but as a Disciple of War requires TP (DRG is an infinite wellspring of endless TP anyway) and positioning, making it a far more sustainable DD in relation to Black Mage but ALSO requires considerably more skill.

I will give you the sad news that you will need to gain a fair few levels in Archer to realize either of the those jobs to their full potential (mostly due to Quelling Strike and Chameleon which respectively reduce your attack's enmity for one move and reduces your current enmity), but both jobs also have their own enmity dumps (Freeze, a damage+negative enmity spell and Evasive Jump, that moves you backwards and reduces enmity).

Note: I play a Dragoon is pretty much any high-level content I go to, btw