1. A computer-implemented method comprising: using a computer hardware processor to perform steps comprising: presenting one or more story units having a particular type to a plurality of users of a social networking system in an initial configuration, wherein a story unit includes one or more stories describing actions performed by a user of the social networking system and having a common characteristic, wherein the actions described by the one or more stories in a story unit are defined by an external system connected to the social networking system; presenting one or more story units having the particular type to an additional plurality of users of the social networking system in an alternative configuration, the alternative configuration being different from the initial configuration; capturing different types of interactions by more than one distinct user of the plurality of users of the social networking system with the one or more story units presented in the initial configuration; capturing different types of interactions by the additional plurality of users of the social networking system with the one or more story units presented in the alternative configuration; associating weights with different types of interactions performed by the plurality of users of the social networking system with the one or more story units presented in the initial configuration; generating an interaction score for the initial configuration based on a number for each of the different types of interactions performed by the plurality of users and the associated weights; associating weights with different types of interactions performed by the additional plurality of users of the social networking system with the one or more story units presented in the alternative configuration; generating an interaction score for the alternative configuration based on a number for each of the different types of interactions performed by the additional plurality of users 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 a story unit having the particular type to a viewing user in the selected default configuration.