I don't see why I would pick any result except of the purple (last one). Not only it gives you an extra Ironbound, but also allows you to move that Changeling off the map in the same turn, even without Dash! Other options (especially the yellow one) seem so much inferior to it.

Green might be awesome if the heroes have particularly terrible willpower. Yellow is really only worth it if the OL has a killer card he's trying to draw- otherwise, there's not much point. Purple is a good choice in most situations.

Another reason (possibly) not to pick purple is because the heroes may be expecting it. Surprise is a fantastic weapon.