As for the tower to choose, we stayed in the Coral Tower last year, thought it was fine. Room was quite large, well decorated, very clean, balcony. It really depends on how much time you spend in the room. We are up and out early, and generally don't spend much time in the room, so couldn't see spending that much extra for Royal Tower when there's really not a tremendous difference.
Also, I think the Coral Tower is more conveniently located, right in the middle, close to the beach, and easy enough to get to any of the pool areas you prefer.