Under the current senate voting system you can either vote for one party above the line or take the effort to allocate preferences to all the candidates below the line and risk your vote being declared informal. Voting above the line means that the party machine allocates your preferences on the basis of wheeling, dealing and questionable trade-offs. Steve Fielding became a Senator because Family first convinced Labor to put them ahead of the Greens.
There would be less scope for questionable practices if voters had the option to allocate preferences by party above the line. (Preferably optional preference voting so we don't have to choose between micro parties that we know nothing about.)

Welcome, lets hope you continue to contribute.
On this occasion we agree, my thread are upper houses democratic is evidence.
I think every voter should be free to preference without others interference.
Including his/her party.
And said this is one answer but still consider we do not need upper houses.
Show me what QLD has lost by not haveing one from 1956.

John D, I agree totally that the voter should be able to declare preferences, as they see fit. That is; as per the optional preferential system.

There shouldn’t be any above and below the line options for the senate, there should just be the one setup, with the voter free to mark as many squares as they wish.

There should definitely be no wheeling and dealing and placing of your preferences where you don’t want them to go or don’t know where they might end up when you vote! That sort of thing is just plain antidemocratic! It is tantamount to stealing your vote. Not quite as blatantly as with the disgusting compulsory preferential voting system, but not far off it!

The voter should have full control over their preferences!

Yeah, not sure if (or how) that would work.
As Ludwig pointed out on another thread, with the OPV system if no preferences are allocated then votes to weaker candidates are simply discounted.
Unlike local elections where there are usually only a handful or less candidates, the Senate offers 76 seats, 12 in each state, with an almost unlimited number of possible candidates.
Given the number of parties/candidates usually offered, OPV would I think be more likely to approximate the current Above the Line situation; ie eliminate the smaller parties, yes, but even the larger players could still get in with a minority of votes.
While I'm not in favour of compulsory voting -actually forcing people who are too disinterested in politics to study the policies to make decisions affecting us all; crazy!- once you're in the voting booth compulsory preferential voting makes sense to me, to ensure your vote will be counted.
Or at least say, 3 preferences.
This is simply the rules of the game. If you want to play...
If you want to play tennis, you have to abide by the rules. Otherwise you're not playing tennis, you're just mucking around with a ball and a racket.
As I have indicated before, I very much like the 50%+1 rule.
The issue here is, I think, not so much about individual voter preferences, but party/candidate preferences, and whether or not those preferences should be disclosed and locked in before the election.

I don't think that the preferencial system can be "fixed", better to abolish it and adopt pure PR.

Yes, Grim, compulsory voting is another hare-brained idea.

This LP post discusses the factors that influenced the "unintended informal vote" in the last federal election.
http://larvatusprodeo.net/archives/2010/09/01/reducing-the-informal-vote-guest-post-by-john-davidson/ One of the messages was that the number of informal votes went up as the number of candidates increased. Forcing voters back to the old style system is a clumsy way of avoiding the allocation of preferences by party machines.
There is no practical reason why the system couldn't be changed to allow preferences to be allocated by voters (not parties) above the line. It would be desirable to allow voters to make excursions below the line if they really want to change the order in which parties have ranked their candidates or they want to vote for a particular candidate.