The best world Major Leagues has ever seen (IMO) is
Hardball Dynasty – Fantasy Baseball Sim Games - Player Profile: Chris Nen.
Others more recently have come within shouting distance of some of his stats, but they've done it in a much more pitcher-friendly era of the World. OPS in Nen's heyday was .050 higher, so his stats are all the more ridiculous. Plus it was the AL, so facing the DH instead of pitchers.
He still holds these World records:
In a season (season number)
Wins (top 3 are all Nen) - 31 (8), 28 (3), 26-t (4)
ERA - 1.15 (4)
WHIP - .080 (3)
Quality starts (top 2 and 3 of top 4) - 37 (3), 36 (4)
OBP allowed - .223 (3)
Also has the highest career winnings percentage (.744)