Ranking/polling field or webform module
Rather than use a field for polling, I would recommend using a polling entity created by a module specific to polls. There is a core poll module.

There are also many contributed modules, the choice would depend on your use case: Advanced Poll, Poll Improved, Poll Extras -- and Poll Blocks provide a block for every core poll.

Then add some theming to make the selections draggable. I have created front-end doodads that populate a hidden element on the page - even an entire node body - so you could register the selections that way if you cannot theme the actual poll items.

You may need to use panels/views/context or template file to add the poll to your page.

My favorite place to search for Drupal contributted modules is http://drupalmodules.com/search/node/poll