> The most widely known preferential ballot is Single Transferable Vote and its cousin the instant-runoff.
> Many election theorists, however view these as the worst possible system.

Can you give me a reference for this? You correctly point out that STV is pretty complicated and can confuse voters; does it have worse problems than that? Several countries are using it; if there are serious problems it seems like someone should have run into an example by now.

Wikipedia notes that strange things can happen if a party fields too many or too few candidates, but (particularly in the case of presidential elections!) this doesn't seem like a serious bug.