#1 Brock Lesnar

It is ambiguous whether the current Universal Champion, Brock Lesnar, will remain in Vince McMahon's billion dollar company, but if he stays, Batista could be an ideal opponent for the Beast Incarnate. Though the two men have been part of WWE for years, they never managed to lock horns. Their only bout was at OVW, which was the developmental territory of WWE in the past.
Brock Lesnar is set to put the Universal Title on the line at the Show of Shows in New Jersey. He will fight the Men's Royal Rumble winner, Seth Rollins. With the speculation to leave WWE after WrestleMania, Lesnar has a big possibility to lose the belt at Metlife Stadium. Considering the star power of Lesnar, Vince McMahon will do everything in his capacity to keep him in the company.
A match between Lesnar and Batista is undoubtedly a dream match for the WWE Universe. It could be a fresh rivalry as they have never crossed paths. Since Lesnar is a part-timer, he is not likely to fight in every PPV following WrestleMania. Hence, Batista and Lesnar could headline SummerSlam this year.