Seed Bomb or Wood Hammer, depends.
Wood Hammer only if you also have Synthesis or Leech Seed. That high damage is great, but you need a way to beat the recoil. Or you can just use Wood Hammer to activate Torterra's ability.
Otherwise Seed Bomb. It has no recoil and good power.
Not Razor Leaf, too low power to be used when you have Seed Bomb instead.