I don't know how I'm voting for certain yet - I want to hear the debate. My thinking at the moment is I would like equally sized constituencies, but with two MPs instead of one in order to introduce competition so the MPs' monopolies end and mean they have to work harder to 'gain market share' to secure re-election next time. But that is not what is on the table.
AV won't deliver this, as it only works with single member constituencies, which means that AV is not proportional representation, it is more like the current first-past-the-post-system but you don't just one chance to vote, meaning 'every vote will count'. Lib Dems don't really want AV, they want 'Single Transferable Vote' like they use in Northern Ireland and Scotland and in some parts of the EU for election to the European Parliament (Governments were given a choice between STV and the list system - ours chose the list system - under this it is more difficult for the public to have influence and the bigger parties are therefore better off).
While AV will give the public the opportunity to vote for their preferred party and tactically at the same time, meaning if you wanted to stop the Tories and Lib Dems getting in and you were a socialist but not to keen on Labour you could vote Socialist Labour 1, Plaid 2, Labour 3, then if Socialist Labour got the lest votes, you vote would go to Plaid, then if Plaid got the least votes your vote would go to Labour. It may mean that in the next rounds Labour would get over 50% of the votes - more votes than the Tories and Lib Dems - so would get elected. However, it could also mean that people could vote Socialist Labour first without the fear of the Tories or Lib Dems getting in because of they vote being worthless as it is under the current first-past-the-post system, as AV would mean the party with over 50% of the vote would get elected. The same applies to other minor parties, such as the BNP, which should make us consider the consequence of voting yes, even if it gives us more freedom to vote for who we want.
I don't know why the big parties want it, it will give the public more freedom to vote.