I don't have a strong opinion toward what voting system future General Elections will use. I don't think that who gets elected is very important: voters don't have any control over immediate policy; they only have influence over the long-term direction of policy, and that doesn't depend on who wins any given election.
However, I used to be very interested in voting systems, and I have an intense dislike of bad arguments. The bad arguments in the AV debate come mainly from the No side.
The silliest is the cost argument. They claim that a switch to AV would cost 250 million pounds. That is highly improbable, and includes the cost of the referendum itself, which is a sunk cost in any case since the referendum is now going to happen. But just take it at face value for a moment.
Assume AV is an improvement — if it is not then the cost argument is irrelevant. 250 million is about five pounds per voter. The average voter will probably have the opportunity to vote in another six or seven elections. If a significant improvement in the value of a vote is not worth a quid, then what is a vote worth? The only people who should be influenced by the cost argument are those of us who believe that voting is worthless anyway.
There is also talk of voting or counting machines; that is a much bigger and easier argument than AV itself. Introducing machines is a huge mistake. FPTP hand-counted is far superior to AV with machines, since there is no reason for anyone ever to trust the machines.
A bizarre gem came from John Redwood, who wrote on his blog, "we think it undesirable that elections are settled by the second preference votes of those who vote for minor or unpopular parties". He doesn't say why. If you like your local independent, or Green, then the fact that you also prefer Conservative to Labour should therefore be of no interest?
A more cogent objection is that AV would produce Labour/Lib Dem coalitions into the indefinite future. I do not dismiss that, but I think it is mistaken. For one thing, the current situation shows that the support for the Lib Dems, being as it is a historically-produced random collection of highly disparate groups, with no policy positions in common at all, cannot survive the Lib Dems actually holding any power. But more to the point, the biggest effect of AV is within the parties themselves.
In 1981, a handful of senior Labour figures broke away from the party to form the SDP. That was only possible because of the utter failure of the previous Labour government, and the sheer disarray that the party was in. The SDP held a handful of seats for a few years, then merged with the Liberal party.
But imagine how much easier the job of splitting a party would be under AV. The problem the SDP faced was that for most Labour supporters, voting for the SDP instead of Foot was more likely to produce a Conservative MP than an SDP MP. AV greatly lessens that effect: if 50% of voters prefer Labour to Conservative, it is almost impossible for the Conservative to be elected because of the Labour vote splitting between two rival factions.
In fact, other factors might turn out more important than the voting system itself: in the face of the threat of splitting, I would not be at all surprised to see steps taken to defend the leadership of parties from internal dissenters. Pay particular attention to rules on party funding or ballot entry.
I think AV would give voters slightly more influence than they have now. I am quite unsure as to whether that's a good thing or a bad thing: the Establishment in this country does damage in internal competition and through its religious attachment to Universalism, but on the other hand it is generally less stupid than the voters. So at the end of the day I am in the Whatever2AV camp.