We use Emojics to collect feedback at the speed of light. Really nice product and service, easy to use and our user love it :) (everyone love emoji). We use also other kind of tool but this is the one with the highest conversion rate, we have an average of 30% visits to feedback.
They have to kind of widget the floating is perfect to ask feedback about the service or a specific page (home page, thank you page, pricing page) and the inline widget perfect for ask feedback about our blog contents. There are a lot of customizations options, we can choose from a tons of different emoji designs, hide the percentage, change the call to actions.
Another interesting thing is their lead generation feature in fact we can ask user contact information after the user click on a specific emoji or instead we can give a coupon code if the user leave us a bad feedback.
They have a free package that we used for start but the pro is definitely better and quite cheap.