The primary benefit of AV is that allows voters to give more information about their desires. In particular, since there is no requirement to fill in all preferences, by leaving parties blank that you definitely do not want to see in power, extremists are excluded. Unless a candidate can gain the goodwill of a majority of voters, they will not be elected. It is not a perfect voting system, but it is better than first past the post.
The "No" group have really run a very dirty campaign. Their lies may be taken to court. They have not revealed their sources of funding. They claim that the BNP will be more likely to be elected. Not true: the BNP are the only party officially endorsing the "No" campaign because they know that they will be wiped out in a system that requires any candidate to gain the trust of 50% of voters. They claim that it will be more expensive because voting machines will be needed. Not true: Australia has had AV for eighty years without machines. I have been employed as a returning officer doing the counting. It really is very simple. They say that voters will be confused, which I find quite insulting as it implies that voters don't know how to count to five. Indeed, if anyone really is confused, they can simply put a "1" for their first preference and leave the rest blank, giving them the option of continuing to vote as they always have. They say that AV gives people more than one vote, which is a half-truth. Yet insofar as people get more than one vote, everyone's vote is recounted every time. It is just like having multiple rounds of an elimination election condensed into a single day. The "no" vote have (as far as I am aware) never answered how it is that the method used to elect party leaders (AV) is deficient for the nation as a whole.
The "Yes" campaign are guilty of overselling, as though AV is going to singlehandedly reform UK politics. It won't but it's still an improvement. A "Yes" vote is a vote for a system that lets voters have more say, a system that recognises the UK is no longer a two-party state (35% of voters at the last election voted for someone other than Labour or Conservative), a system that excludes extremists by preventing candidates with strong minority support being elected without majority backing, a system supported by the leaders of the following parties: Labour, Liberal Democrats, Greens, SNP, Plaid Cymru, UKIP. The only leaders who are supporting the "No" vote are the Tories and the BNP.
Vote "yes" tomorrow.