i've maxed out all the stats before but i tend not to do it through the game. i just play through it then max everythig out at the end. triple AP weapons help ofc. cactuar valley is a good AP spot as its possible to get over 100,000 AP in one battle with triple AP weapon. however, the quickest, though not necessarily easiest, way is the don tonberry trick.

wait until ur trying to max out ur luck stat, that is a right cow!