Iconic is generally accepted to represent something that the layman would recognise. Irrespective of the artistic merits of the ornate/draped G4 and W4 reverses or any other design familiar to ourselves, Joe Public wouldn't recognise them. It's likely to boil down to a few popular designs such as the wren reverse on the farthing, the Soho cartwheel or the bronze penny featuring the Britannia reverse, a George and Dragon reverse coin, an Elizabeth 1st obverse, and something like a Cromwell obverse. Basically all something the public could identify with relative ease for many people.