It sounds like a tough decision. If you're concerned about letting a potential Ling app, I would ask the mods what they would think about GreedLing before making your decision in case that might influence it. They are two separate characters, but with them sharing the same body, I'm sure that complicates things.

My Ed is from the Briggs arc, so he would recognize both of them if that helps you any. (Hopefully it doesn't make it harder for you to choose!)

In the end, it might be best to go with which version you think you would enjoy the most.