#1 Lars Sullivan
While we've repeatedly mentioned that John Cena's limited appearances should be used to face fresher opponents, one of the few exceptions to that rule is Lars Sullivan. Cena was supposed to face Sullivan at WrestleMania 35, with the build reportedly planned for the start of 2019. However, Sullivan's anxiety attack kicked in and his debut was delayed until after WrestleMania 35.
Last year would have been the perfect time to introduce him but a lot has happened since then. Not long after debuting, Sullivan would suffer a major knee injury that would keep him out an estimated 6-9 months. What made things worse at the end of 2019 was new information released revealing Sullivan's previously-unknown past in adult films.
While we don't wish to shame him for that or hold it against him, the reality is that the circumstances won't be favorable for him once he returns. Unless WWE pulls off a miracle, he's likely going to lose his momentum and Cena shouldn't be putting over someone whose push could be at risk.