While I understand reasons for more types of mounts in mmo, in FF mmo I couldn't care less for any other type than chocobos, that's probobly cos of Final Fantasy fetish ;D

Anyway my idea would be different races and types of chocobos, like for example:

a) Battle Chocobo = massive muscular more, deff but slower.

b) Race Chocobo = slim light, and fast.