The location will determine the balcony size. I believe those on deck 10 are deeper (larger) than those on the other decks.
I mini also gives you a few more square feet over a balcony. It doesn't sound like much of a difference, but the way the cabins are laid out helps with the flow. I realize you didn't ask, but if you have 3 people I'd chose a mini over a balcony just because of the square footage.