The majority use a single number above the line. That means they're letting their selected party determine where preferences flow, according to group voting tickets. Group voting tickets that most people never see, unless they're interested and proactive enough to visit the AEC site.
I seem to recall a time when how to vote cards showed the group ticket in grey under the line. I don't think they do that now.
Preference deals suck. Voters certainly have a say as to who is elected, but it's significantly influenced by preference deals. Now, perhaps there's no realistic way to end preference deals, but I do not understand why we can't number multiple boxes above the line.
Don't agree with your party's preferences? Just number the 23 boxes in order of your own choosing.
Does your party have a split ticket, but you want to choose which major party get your preferences? Number the boxes above the line.
On a related note, I could have sworn I numbered up to 70-something. Either I numbered wrong, or I remembered wrong. Hopefully the latter; I don't want it said that my vote was responsible for electing one of the many nutcases vying for last place on my big white sheet...