Uncertain. Achilles abilities and limits are still being defined, narratively...
Hazzarding a guess, I would *think* that, armed with Athena's Spear, Achilles can take a majority; without it, it boils down to exactly what "god-level" DC Hercules is being portrayed at: if played up, he likely will take the majority; if played down, then Achilles' Divine Grace ability will give him an edge similar to Diana's speed in terms of dealing with Herc, but it won't be a definitive thing.
Generally speaking, Achilles, though not to the degree that Diana would win; if strickly H2H, then Herc has better odds...