It really depends on who is the "Meridian Child" (the leader of your party). If Kevin is, Archmage would be the way to go (because of her more powerful Saint Beam that might be useful in the final area of Kevin's scenario). If Hawk is, I'd say go Rune Master. If Angela is, go Grand Divina.

Either way, I think Archmage would be the best because if you get Poto Oils, she'd make a pretty decent healer if that was necessary. But if you want spell power, I guess Rune Master would be a good choice. Grand Divina also makes a good choice, for she is the strongest offensively out of all Angela's final classes, and she's got a decent intelligence level.