To me, the biggest weakness of
PR is hilghlighted by the party system in Italy since Mussolini, and in France before de Gaulle....
But the best way to decide on it would be by referendum. That said, it's probably a waste of energey discussing it here. I'm fairly certain a British public would reject
PR, firstly because Brits like their institutions, and Westminster-style democracy is one of them, and secondly, because folks are likely to vote along party lines, and the Tories and Labour are bound to campaign against it.