I always felt that Final Fantasy IX's script does the absolute best job of balancing tone. Whereas in other titles (such as Final Fantasy VII and VIII) the moments of levity are often tonally dissonant and jarring, I feel that the ups and downs in FFIX are handled very well. It's all very organic, and I can't think of any moments that feel particularly forced (like the oft-cited, god awful laughing scene in FFX).