FFIX's Steal felt the least rewarding for me, since you'll spend most of the boss fights just turtling until the lousy RNG decides to give you the items, which often have terrible drop rates. FFX's Steal was pretty useful, not to mention it has tactical uses for breaking Machina and stopping enemies from using Auto-Potions. FFXII is the one where I used Steal the most, and it really makes a difference in the amount of sellable Loot you obtain.