For grinding Daddy WarBugs, use the T8 Battle+Pesticide on level 3:3. Just keep shooting it/blocking it with your shield and you'll be done with the level in about 15 minutes, netting ~55k every time. It's got the most bosses/ant hills/waypoints which are the biggest experience gains.
~Alan | Anime
I award you no points, and may God have mercy on your soul.