How do you tell whether AV is more or less proportional without using a completely arbitrary way of weighting first and second choice preferences?
In theory, by looking at how it distributes seats to various parties and comparing that to polls of people's preferences. The consensus seems to be that AV will favour 'centrist' politics, tightening the stranglehold of Tories, Lib Dems and Labour on parliament and ignoring any views beyond those groups.