This is splitting hairs, but I think Super Bowl 49 was a better game to watch, start to finish, than 51. It was always competitive down to the final seconds, both teams played great and had big plays on both offense and defense, the Seahawks were a team of swaggering trash talker bullies you loved to hate, it was the Thrilla in Manilla of football.
Plus you can't overlook that the Seahawks were the defending Super Bowl champs who had HUMILIATED Peyton Manning at the end of his greatest individual season the year before. For Brady to turn around and beat them the very next year was a pure delight.
Super Bowl 51 was just this impossible amazing insane THING that somehow happened anyway. As an accomplishment the 28-3 comeback has no equals, but as a game it was 2.5 quarters of getting crushed by the Falcons, 1.5 quarters of madness and an overtime cakewalk. Once the Patriots won the coin toss a billion people went "Well, the Falcons are dead" all at once, including everyone on the Falcons. Plus really, who gives a crap about the Falcons themselves?