Voting system -- user field or content type


I am creating a voting system for pictures and I want to get advice as to what the best way of building this.

I have come up with two ways:

  1. Modify User model to include a “vote” field to record a person’s vote.
  2. Create a Content Type that registers a person’s vote. I guess each record will have 1) which picture that person voted for and 2)a link to the User’s id.

The number of votes for each picture will be displayed on the front end, and the user should be able to change their vote.

I am wondering what you thought the better way was?