Although information system acceptance has received considerable attention in the past two decades, prior studies on competing products are still relatively scant. In the new era of Web 2.0, consumers face with a wide range of products with similar functions and purposes, and therefore, they have to make choice among these competing technologies. Drawn from media richness theory and social identity theory, we develop a research model to investigate the alternative behavior that occurs in the competing products. An empirical study is conducted in two competitive social media platforms, i.e., light-blogging and micro-blogging. The results demonstrate that social identity positively affects we-intention in both light-blogging and micro-blogging. However, the impact of media richness on social identity in the two competing products are different. Specifically, three constructs in media richness, i.e., immediate feedback, multiple cues and personal focus positively affect social identity in light-blogging, while for micro-blogging, only immediate feedback and personal focus take effect. A relative model was further applied to explain users’ media choice of competing products. The findings reveal that the relative perception towards immediate feedback, language variety and personal focus across the two social media will positively predict users’ relative social identity, which further leads to their relative we-intention to use. In this regard, the relative model suggests that social media companies should focus their efforts and tactics on the relative advantages, as compared to their competitor. This study highlights the importance of applying the relative model into investigation of competitive social media acceptance , and is expected to shed some new lights on both research and practice.