Merric, Wendell, generics or some reclassed schmuck. You won't need to use the warp staff that early
Ch. 3 has mountains pretty much EVERYWHERE.
Ch. 4 is a very long stretch of land, separating you with a Cav Rush. Oh, and Thief could instablick the south village, killing Merric.
Ch. 5 has Diaper Head and his merry men trapped, though you might not need warp for this. It just makes things easier on yourself if you're trying to save all of them.
Ch. 3 = Sheeda
Ch. 4 = Sheeda
Ch. 5 = Sheeda
Is anyone else seeing a common theme?