The GBA version of FFV is portable; it has the auto-dash feature; and it has a bestiary. I haven't played Anthology, so I can't describe it, but the original FFV doesn't have any of these conveniences.
It also has a few new classes which are arguably superfluous and in one case grossly overpowered against most monsters. However the bonus dungeon is actually the best designed one I've known of the GBA ports.