Hint: not Justin Bieber.
BuzzFeed ran the most recent ten tweets for each user through Online-Utility’s readability calculator (after stripping them of hashtags, links, and @ replies, which confuse the program). The calculator uses cues like word length and sentence complexity to determine the grade level a piece of text would be appropriate for. Barack Obama triumphed, followed by Katy Perry and Lady Gaga. All these scored around a sixth-grade reading level.
Justin Bieber came in dead last.