Which voting system is best?

The answer to this is that there is no clear winner for the title of 'best', it depends on the criteria you think most important; so part of the argument is what constitutes a good balance of advantages and downsides. However, as to what are the upsides and disadvantages, well you could do worse than to look at the front running options here with a fair-looking set of assessments. LabourList poll: Which voting system is best? | LabourList.org