The safest boss to spawn from is definately Laiden (or Ivid Laiden for A runs in crespo).
The one that gives the most XP is Yoshima Diamechi, on Space of Pilgrimage. But he is somewhat regularly checked on by GMs, so you are taking a big risk.
Oread is really the only other option. I don't know of any other boss that spawns mobs that give XP. And GMs don't watch him nearly as closely as they once did.