It depends on John Cena, I think. Whether it was Brock Lesnar, CM Punk, Daniel Bryan, Seth Rollins, or AJ Styles, all of them have gone over Cena around the summertime, which immediately catapulted their credibility and stock much higher, in my opinion.
Anyways, I do believe that the summer of 2016 belonged to Styles, despite Dean Ambrose being the WWE Champion at the time. However, in regards to 2017... I could really see the WWE make it the "Summer Of Finn Balor," even though it shouldn't be. :sleep Honestly, it should be either Baron Corbin (with the MITB Briefcase) or Braun Strowman.