Resume says Surfer, though if we use common opponents, Apocalypse might have a shot. Apocalypse needs more appearances outside of X-Men related books where he interacts with other top tiers (like Thanos or Maelstrom). On average he's somewhere in the range where characters like Hulk, Stryfe, Living Monolith, and Prince Thor are below him, and he can hold his own against High Evolutionary. That's not enough to say he'd beat Surfer with any consistency given the tale of the tape. Surfer has a lot more tape.
That's true. But Surfer has messed with people's genes before. In fact he's evolved an entire planet's population billions of years forward, forcing the planet's population to grow themselves to death. If anyone has the raw power and matter manipulation skills to screw with mutant genes it's Surfer.