A digital magazine server receives user comments on content items of a digital magazine and generates comment threads. A comment thread has one or more user comments associated with a content item and at least one topic. A topic thread on a selected topic includes one or more comment threads related to the selected topic. To select comment threads for a topic thread based on the selected topic, the digital magazine server determines the relevance of the topic of each comment thread to the topic of the topic thread and determines the quality of the comment thread based on a plurality of quality factors such as number of comments and timestamps of the comments in a comment thread. The digital magazine server aggregates the comment threads based on at least one of topic relevance determination and thread quality determination and selects comment threads based on the aggregation.