The weather and the vistas on a Greek Island cruise definitely call for a balcony cabin if at all possible. And as janfred pointed out, when you break it down, the balcony cabin isn't that much more per day than an oceanview. I've even seen some sales recently where the o.v. and balcony were actually the same price.
I would select A423 if available because it is a little farther from the elevator lobby--not that that is a big problem; any of the three would be fine.