As far as i know they all give the same amount of exp based on the chocobos current rank after feeding it witch ever food each Hr. Curiel Root will give the chocobo exp buff agents mobs but not the food you feed it.

If your chocobo is at regal purple try:
4 × Apples, 10 × Pears, 10 × Berries

Try alternateing the fruits when feeding to the chocobo. Maybe like 5 pears then 3 berries 2 apple etc.... till you feed them all to the chocobo.