#1 Roman Reigns vs. Braun Strowman

There was never any doubt. In a year that gave us many great feuds, this one was the clear gold medalist. Its ramifications will be felt for years to come.
Throughout the months these two were rivals, they tried to kill each other at every turn - literally. It was an intensity rarely seen in today's era and drew parallels with WWE's Attitude Era peak, which Roman Reigns subtly acknowledged in a promo after he backed an ambulance with Strowman trapped inside into a truck, crushing it.
Every match was brutal. The two competitors have great ring chemistry together and they never disappointed in any match or promo, and though it may have been bordering on repetitive, as it lasted on and off for two-thirds of the year, it was hard to notice because everything about it was so good, and each encounter gave us something new.
Most importantly of all, it elevated Braun Strowman to the main event level, a status that SummerSlam confirmed and made permanent. Roman Reigns, too, benefited immensely, as it was his best singles feud to date. Always a victim of being pushed too hard, too soon, Roman Reigns just wasn't ready to be "the guy" in 2014-15, but he is ready now, and this feud was arguably a major part of that.