The AV referendum is a completely fake choice. It's like asking us all 'Would you like a rat burger or a slug sandwich?': there's no option to say 'No, actually they both sound gross, I'd like a caesar salad please'.
We're all sitting here debating the pros and cons of rat burgers versus slug sandwiches, but the reality is that neither option is nice or particularly desirable.
The reformers have been massively stiffed. Clegg's condition for joining the coalition was a referendum on electoral reform. But what he's ended up with is a referendum that asks us to choose between the existing fairly shit system (rat burger) and a new, more complicated, basically just as shit system that won't actually be any fairer (slug sandwich). In the process any opportunity for meaningful electoral reform has evaporated.
A Yes vote is a vote in favour of some apparatchik dicking around with the existing shit system in order to implement a similarly shit system which will cost vast sums to implement, for just as many safe seats, even more byzantine tactical voting and the exhaustion of political will for electoral reform for another century or so.
As The Economist says, the only reason to vote Yes is because it might be a step toward PR; but such a massive constitutional change as this should be voted in on its own merits, not because it might eventually lead to something else. So given that the available choices are bullshit, I would prefer to stick with the existing system in the dim hope that eventually a meaningful alternative will be proposed.
In a nutshell, I don't want either a rat burger or a slug sandwich, but if that's all that's on offer right now I'd rather stick to what I know and concentrate on campaigning for a proper menu.