This paper presents the results of a study that examines the factors that influence travelers’ mode choice between transit and ridesourcing, for two distinct market segments—transit users in a regular context and auto users in occasional situations when a private vehicle is not available. Data from a stated preference (SP) survey were used for this study. Specifically, responses to a set of attitude-related questions were used to extract latent attitude factors that represent various aspects of attitudes toward mobility options. Mixed logit models were developed for the two classes. Socioeconomic and demographic attributes, as well as the attitudinal factors, were explored as independent variables. Model results revealed distinct behavior patterns between transit users and auto users. For transit users, the decision to shift to ridesourcing is highly affected by the perceptions of time and cost as well as motivations for technology, while the concerns on traveling with strangers and joy of driving were major barriers for auto users to use ridesourcing. Auto users would use ridesourcing when they believed that they would receive higher utilities, in relation to time, cost, reliability, convenience, comfort, stress relief, and so forth. This study provides further insights into the contributing factors to the choice between transit and ridesourcing. The results present a better understanding of the potential market for ridesourcing and highlight underlying attitudes that have significant influences on choice behavior. The findings could be helpful for planners and service providers to better plan for and address the needs and concerns of travelers.