Gloria gets you access to Lodge Gloria (once you slog through the veiled dating simulator bs raising the friendship to 100), netting you two units instead of one.
However, I had read that Gloria is really only useful at 5/5, so I picked Lucas and Dialga to get a unit with dragon zone, since I skipped Nate and Haxorus (who I think can set it up, but maybe I'm misremembering).