Ranking systems seem superior to non-ranking methods of voting. This is due to votes not being wasted. If your top ranked person doesn’t get in, and there isn’t already a clear winner, your second placed ranking will count. This means FPP and MMP should be crossed off the list leaving PV, STV, and SM. [Edit: I've just discovered that I misread the info - SM IS NOT A RANKING SYSTEM. However, it is good because, like MMP, it is a good combination of local and nation-wide representation]
If we didn’t have a party system, I would prefer PV because that gives the best local representation. Since we seem stuck with a party system it makes sense to have some influence over the party representation in government. This means we should be considering STV and SM only. [Edit: and MMP if my ranking criteria is out the window - still SM + ranking would be good]
STV requires a coalition to be formed on most occasions. This gives “extra” influence to smaller parties beyond the influence they deserve from the votes. I don’t think this is fair. [Edit: Likewise MMP relatively more often requires coalitions, and with parties that are over-represented because of so many list seats available]
SM doesn’t usually require a coalition which means smaller parties have the influence in parliament at the same level as the number of votes they received. [Edit: and those smaller parties do have influence which is important]
From this analysis, SM (Supplementary Member) seems like the best system of voting. So vote for a change in voting system and vote for SM.
My analysis began by forming a table [Edit: Table will be updated to fix my error but I will keep the original available] (link goes to a Google Doc you can print for easy reference). I used the information sent out to all registered voters in the election pack. If you prefer more detail you can read what the Maxim Institute have to say. My view was not influenced by their conclusion that SM is the one to pick. I came to my choice independently. A quick look around the Internet has failed to turn up anything from the political left on the voting systems. There is the campaign for MMP group perhaps, but they don't seem to realise that all of the benefits of MMP and more are available under SM.
Maybe I'm way off. If you think so, let me know and let me know why you think this is so.