rotiart
Stan Lee Stole my name
Marvel
LongTerm, I'd say Thanos. 1. Thanos. He knew about the HOTU during the Infinity Abyss saga, but didn't do anything about it until Marvel: The End. He knew what players to grab when Warlocks good and bad sides went bonkers. He also grabbed "supreme" power 3 times.
Shortterm, Doctor Strange. In the Infinity Gauntlet series, he knew he'd have to fight Adam Warlock so he grabbed all of his most powerful artifacts and used the Eye of Agamotto to hide them. And was able to overcome the powers of the infinity gauntlets with shortterm prep.
DC
Longterm
It'd be a tossup between Lex Luthor and Alex Luthor. Lex planned for the eventual dead of Alex by Joker.
Shortterm, batman. That guys got mad detective analytical skills.