Both suck late game (Starting around 50 and on) at DPS. Not meta talk, just purely on a "fun"/fight standpoint...they both feel very weak, unless you're geared out the wazoo. I made a Summoner my first go, and I found myself just clearing waves without much Ironworks and or other bought gear. Which makes sense of course, its the Warlock of FF, but even the Black Mage feels like a howitzer compared to....well two actual howitzer classes in the game.

Bard feels like it requires a pet and or a solid aura buff. And Machinist feels like it needs a stronger pet in general. I love the idea of the Machinist, I just hate the implementation, especially late game. With all that considered...go Bard, not only will you be buffing your teammates, but also debuffing the enemy. Also who doesn't like a nice tune while slaughtering your enemies?