Defintely a eraser if you use anything else it just seems to keep coming back. I did hear of a product made by either meguiars or Mothers called back to black that's supposed to work but I haven't tried it yet.
back 2 black is NOT made to take off or cover wax in black plastic trim! it's made to restore older black trim that might be a little faded or worn. it's more of a dressing than a cleaner, really. if you use it, it might cover the wax, but it'll show up again once the back2black wears off.
i got some stuff from some lady that was selling shit door to door.. its soon kinda of all natural cleaner.. and you can even drink the shit.. well it cleaned up my door trim nicely.. got all the wax of it.. and eveything else you can think of... i cant remember the name of the stuff.. ill get back to you on that