Pet Leveling Tip
Regardless of the dungeon you choose, and regardless of the amount of attacks that your pet does, the EXP will always end up the same when you complete the dungeon. That said, go to the shortest, easiest dungeon - Trial Forrest. Stay with 1 star. Complete the quest. You can get from 1 ~ 10 in under an hour, and 1~20 in under half a day. It's boring, but it's fast if you want to get your pet to it's evolved form.
I've read it somewhere in the lobby ages ago, but since I haven't seen it posted here, might as well let people know. Credits does not go to me.