Our preference probably comes down to what we're familiar with, which seems to mostly be Final Fantasy, Final Fantasy VI, and Final Fantasy VII. Most of us at least know of Final Fantasy X/X-2, Final Fantasy XIII, and Dissidia Final Fantasy, and a few of us know Final Fantasy XIV: A Realm Reborn's characters, but that seems to be it.
Personally, I'm just familiar with Final Fantasy, Final Fantasy VII, and Final Fantasy XIV: A Realm Reborn. Vivi does nothing for me, and neither does the Warrior of Light, and I can't even picture most of the other suggested characters.
Does that mean I shouldn't be the one making the decisions? Probably, though if I was the one making the decisions I'd certainly do more research than "I want Black Mage".
I will say one thing though: With how recognizable the Warriors of Light from the first game (not the one from Dissidia Final Fantasy) seem to be, I don't think adding them is an inherently bad idea.