Since they nerfed pet leveling by abondaning the daily quest i kinda try to use all trainers for leveling.
So my team usually has one pet to conter the first pet of the trainer, 2nd pet is the Darkmoon zeppelin, because it can kill the last enemy pet with explode, and 3rd any pet i want to level.
The counter pets I use are
FLayer Youngling for Aki
Eternal Strider for Farmer Nishi
Marsh Fiddler for Wastewalker Shu
Emerald Whelpling for Hyuna of the Shrines, Mo'ruk and Courageous Yon
but there are probably a lot of possibilitys
and I just realized I have totally forgotten about Seeker Zusshi and not faught him since 5.1