I got this because it's the one used on wordpress.com. I've only used it for the ratings. Beware: you don't own any of the data collected by this plugin, polldaddy does.
In addition to that, there's limited configuration over the look and feel, I had to use a bunch of very silly css rules and workarounds to just turn certain things off to look better. You can't access the rating data via a theme, so forget about having microformats.
Good if you want to pay $200+ per year.