John Cena's WWE Championship reign will only be successful if he has credible opponents facing him.
Having had feuds and matches with nearly everyone on the current roster, Cena will need new opponents to face.
There are five Superstars who could bring out the best in John Cena. Each of these men also could help to bring a serious side back to Cena's persona.
Honorable mentions of who could face John Cena are Daniel Bryan, Kassius Ohno, and CM Punk.
Daniel Bryan would be an especially helpful foe for John Cena. The technical skill of Bryan would be an incredible counter to Cena's brute strength. Also, Bryan's ability to have excellent and compelling matches would make Cena look stronger in the ring.
There does not need to be a traditional "good guy/bad guy" story here. Fans should decide whom they want to win without elaborate narration in order to keep focus on the Cena vs. Bryan matches.
Ohno is capable of telling an excellent narrative story in the ring with plenty of intensity. His recent match on NXT with William Regal told a fantastic story that revolved around a head injury to Regal and Ohno’s fingers being “broken” during the match.
Seeing John Cena and Kassius Ohno in a feud would provide a huge boost to Ohno’s career and give Cena a brand new foil.
Finally, CM Punk has been an incredible opponent for John Cena in the past and could be again in the future. Their storied feud has provided many memorable moments and matches. WWE could easily reignite this feud at any point.