Chickens are the fastest but there is an area in the post game that has only chicken enemies. It's in the tower Lione takes you to called the Connecting Spire for her side quest. You have to press a button on the top floor which will reveal a ladder on the first floor. If you learn the queen skills of bind and emboldening command, you can at least kill 2 before they escape.
Besides chickens or before the post game, I think the best way to level would be to respec into multi target skills and kill lots of enemies around your level.
Besides chickens or before the post game, I think the best way to level would be to respec into multi target skills and kill lots of enemies around your level.