In my humble opinion, Namco franchises offer:
Fighting character (Tekken)
Fighting character with weapons (Soul Calibur)
JRPG character (Xenosaga)
RPG character (Dark Souls)
JRPG character (Lloyd)
My non-biased stance says Dark Souls sounds like the most unique representation. Although I know nothing from it.
But I also lean a bit on Xenosaga because KOS-MOS looks unique as heck.
My biased stance says Soul Calibur should get a representative, because it's both a 3D fighter, and they use melee weapons. That's pretty unique. Nightmare sounds like an excellent choice because it's another heavy sword character (think Ganondorf's smash attacks but for the whole moveset).
My SUPER biased stance says Sophitia should be the one... But that's not happening as she's got like a dozen of equally important characters, none of them as important as Nightmare, Mitsurugi, or Sigfried.
I like Namco, but there isn't a character that I would like LOVE to see included. Anything's fine for me, tbh. As long as it's fun.