10. A computer-implemented method comprising: using a computer hardware processor to perform steps comprising: receiving a story request from a viewing user of a social networking system; generating a story unit including a plurality of stories describing actions performed by one or more additional users of the social networking system connected to the viewing user, the story unit having a particular type determined from a characteristic common to each of the plurality of stories, the actions performed by the one or more additional users being defined by an external system connected with the social networking system; determining an interaction score for an initial configuration based on user interactions with previously presented story units using the initial configuration, wherein determining the interaction score for the initial configuration comprises: associating weights with different types of interactions performed by more than one distinct user of the social networking system with the one or more story units presented in the initial configuration; generating the interaction score for the initial configuration based on a number for each of the different types of interactions performed by the users of the social networking system and the associated weights; determining an interaction score for an alternative configuration based on user interactions with previously presented story units using the alternative configuration, wherein determining the interaction score for the alternative configuration comprises: associating weights with different types of interactions performed by additional users of the social networking system connected to the viewing user with the one or more story units presented in the alternative configuration; and generating the interaction score for the alternative configuration based on a number for each of the different types of interactions performed by the additional users of the social networking system and the associated weights; selecting a default configuration based at least in part on the interaction score for the initial configuration and the interaction score for the alternative configuration; and presenting the generated story unit to the viewing user using the selected configuration.
10. A computer-implemented method comprising: using a computer hardware processor to perform steps comprising: receiving a story request from a viewing user of a social networking system; generating a story unit including a plurality of stories describing actions performed by one or more additional users of the social networking system connected to the viewing user, the story unit having a particular type determined from a characteristic common to each of the plurality of stories, the actions performed by the one or more additional users being defined by an external system connected with the social networking system; determining an interaction score for an initial configuration based on user interactions with previously presented story units using the initial configuration, wherein determining the interaction score for the initial configuration comprises: associating weights with different types of interactions performed by more than one distinct user of the social networking system with the one or more story units presented in the initial configuration; generating the interaction score for the initial configuration based on a number for each of the different types of interactions performed by the users of the social networking system and the associated weights; determining an interaction score for an alternative configuration based on user interactions with previously presented story units using the alternative configuration, wherein determining the interaction score for the alternative configuration comprises: associating weights with different types of interactions performed by additional users of the social networking system connected to the viewing user with the one or more story units presented in the alternative configuration; and generating the interaction score for the alternative configuration based on a number for each of the different types of interactions performed by the additional users of the social networking system and the associated weights; selecting a default configuration based at least in part on the interaction score for the initial configuration and the interaction score for the alternative configuration; and presenting the generated story unit to the viewing user using the selected configuration. 13. The computer-implemented method of claim 10 , wherein the story unit includes one or more images associated with the plurality of stories.