MP3 I'd imagine would be pretty decent for Priests due to elemental weakness (Assuming. Don't know for fact), and it's a popular map, making things even better due to better Holy Symbol use.
MP3 mobs aren't actually weak to holy/heal, they take normal damage
Jr. Selkies are weak to fire, Slimys are weak to lightning
MP3 mobs aren't actually weak to holy/heal, they take normal damage
Jr. Selkies are weak to fire, Slimys are weak to lightning
Which is why it was so awesome to train my UA WK there. (Y)
Other than suggested, I can't really think of any other good places to train. Maybe try Monster Park or some PQs if you don't like those spots.