Looking over the two versions of the base class, the PF monk seems like a significant upgrade without getting into ACFs for the 3.5 monk.

Abundant step is more than 1/day; the DR is 10/chaotic instead of magic; stunning fist can fatigue, sicken, stagger, blind or deafen, or paralyze; other 1/day abilities run off the Monk's ki pool for multiple uses per day. Style feats and archetypes can make the monk more supernaturally useful with quinggong making you able to cast a few interesting spells for ki points.